Packet Transmission Method, Apparatus, and System

ABSTRACT

A packet transmission method, including receiving, by a session management function network element, first access network tunnel information and second access network tunnel information that correspond to a first service, and sending a downlink forwarding rule to a user plane function network element, where the downlink forwarding rule includes the first access network tunnel information and the second access network tunnel information, and the downlink forwarding rule indicates the user plane function network element to replicate a received downlink packet of the first service, and send downlink packets of the first service through two paths respectively corresponding to the first access network tunnel information and the second access network tunnel information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/CN2019/078176, filed on Mar. 14, 2019, which claims priority toChinese Patent Application No. 201810291412.3, filed on Apr. 3, 2018 andChinese Patent Application No. 201810483377.5, filed on May 18, 2018 andChinese Patent Application No. 201811386638.8, filed on Nov. 20, 2018.The disclosures of the aforementioned applications are herebyincorporated by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates to the field of communicationstechnologies, and in particular, to a packet transmission method,apparatus, and system.

BACKGROUND

A dual connectivity mechanism is proposed in a 5th generation (5G)communications system. A communications system in the dual connectivitymechanism includes two radio access network (RAN) devices a master RAN(M-RAN) and a secondary RAN (S-RAN).

As shown in FIG. 1, in the dual connectivity mechanism, there are twopaths for transmitting an uplink packet/a downlink packet, and one ofthe path passes through (1) user equipment (UE), an M-RAN, a user planefunction (UPF) network element, and a data network (DN), and the otherpath passes through (2) the UE, an S-RAN, the UPF, and the DN.

The transmission path is described using a downlink packet as anexample. When receiving a downlink packet sent by the DN, the UPFnetwork element sends the downlink packet based on a packetcharacteristic. For example, a packet that meets a specificcharacteristic is sent to the UE though the M-RAN, and a packet thatmeets another characteristic is sent to the UE though the S-RAN. Thatis, different packets are sent through the two transmission paths.

With development of 5G, ultra-reliable low-latency communication (URLLC)scenarios, mainly including services, such as unmanned driving andindustrial automation, that require a low-latency and high-reliableconnection are defined in a 5G network architecture. Because most of theforegoing URLLC scenarios are services related to life safety orproduction safety, no error is allowed. In a URLLC scenario, how toimprove reliability of packet transmission through dual transmissionpaths in a dual connectivity mechanism becomes a problem that urgentlyneeds to be resolved.

SUMMARY

Embodiments of the present disclosure provide a packet transmissionmethod, apparatus, and system.

According to a first aspect, an embodiment of this application providesa transmission control method. The method includes receiving, by asession management function (SMF) network element, first access networktunnel information and second access network tunnel information thatcorrespond to a first service, and sending, by the SMF network element,a downlink forwarding rule to a UPF network element, where the downlinkforwarding rule includes the first access network tunnel information andthe second access network tunnel information, and indicates the UPFnetwork element to replicate a received downlink packet of the firstservice, and send downlink packets of the first service through twopaths respectively corresponding to the first access network tunnelinformation and the second access network tunnel information. Forexample, in a dual connectivity scenario, the two paths may be a firstpath between the UPF network element and a master base station, and asecond path between the UPF network element and a secondary basestation. In a single connectivity scenario, the two paths may be a firstpath and a second path between the UPF network element and a basestation.

According to the foregoing method, for a specific first service (forexample, a URLLC service requiring high reliability), the SMF networkelement sends, to the UPF network element, the downlink forwarding ruleincluding the first access network tunnel information and the secondaccess network tunnel information such that after subsequently receivinga downlink packet of the first service, the UPF network elementreplicates the downlink packet of the first service, and sends downlinkpackets of the first service through the two paths respectivelycorresponding to the first access network tunnel information and thesecond access network tunnel information. In this way, reliability ofpacket transmission of the first service is improved.

In a possible design, if the first service is at a service flowgranularity, the downlink forwarding rule further includes a serviceflow identifier of the first service and a session identifier, or if thefirst service is at a session granularity, the downlink forwarding rulefurther includes a session identifier of the first service. Therefore,for services at different granularities, downlink forwarding rules forcorresponding granularities may be provided such that the UPF networkelement can implement more accurate and efficient packet transmission.

In a possible design, the method further includes sending, by the SMFnetwork element, indication information to a base station, where theindication information triggers determining of the first access networktunnel information and the second access network tunnel information. Inother words, after receiving the indication information, the basestation learns that the first access network tunnel information and thesecond access network tunnel information need to be determined. Forexample, the indication information may include at least one of thefollowing a quality of service (QoS) parameter, slice identificationinformation, a DN name, and first core network tunnel information andsecond core network tunnel information.

In a possible design, the method further includes sending, by the SMFnetwork element, an uplink forwarding rule to the base station, wherethe uplink forwarding rule includes the first core network tunnelinformation and the second core network tunnel information, and theuplink forwarding rule indicates the base station to replicate areceived uplink packet of the first service, and send uplink packets ofthe first service to the UPF network element through two pathsrespectively corresponding to the first core network tunnel informationand the second core network tunnel information. The base station hereinis a base station in a single connectivity scenario.

Similarly, if the first service is at the service flow granularity, theuplink forwarding rule further includes the service flow identifier ofthe first service and the session identifier, or if the first service isat the session granularity, the uplink forwarding rule further includesthe session identifier of the first service.

In a possible design, the downlink packets of the first service that aresent through the two paths respectively corresponding to the firstaccess network tunnel information and the second access network tunnelinformation include a first downlink packet and a second downlinkpacket, where the first downlink packet and the second downlink packethave a same sequence number, the first downlink packet further includesa first service flow identifier, and the second downlink packet furtherincludes a second service flow identifier.

In a possible design, the method further includes allocating, by the SMFnetwork element, the first service flow identifier and the secondservice flow identifier to the first service, and sending the firstservice flow identifier and the second service flow identifier to UE.

In a possible design, the method further includes sending, by the SMFnetwork element, an uplink forwarding rule to the UPF network element,where the uplink forwarding rule indicates the UPF network element todeduplicate two uplink packets that have a same sequence number and thatrespectively have the first service flow identifier and the secondservice flow identifier.

In a possible design, the method further includes sending, by the SMFnetwork element, indication information to the UE using a non-accessstratum (NAS) message, where the indication information indicates the UEto replicate an uplink packet to obtain a first uplink packet and asecond uplink packet, and send the first uplink packet and the seconduplink packet over different radio bearers, where the first uplinkpacket and the second uplink packet have a same sequence number. Forexample, the first uplink packet corresponds to the first service flowidentifier, and the second uplink packet corresponds to the secondservice flow identifier.

According to a second aspect, an embodiment of this application providesa packet transmission method. The method includes determining, by a basestation, first access network tunnel information and second accessnetwork tunnel information that correspond to a first service, andsending, by the base station, the first access network tunnelinformation and the second access network tunnel information to a SMFnetwork element, where the first access network tunnel information andthe second access network tunnel information are usable fordetermination of a downlink forwarding rule, and the downlink forwardingrule indicates a UPF network element to replicate a received downlinkpacket of the first service, and send downlink packets of the firstservice through two paths respectively corresponding to the first accessnetwork tunnel information and the second access network tunnelinformation. For example, in a dual connectivity scenario, the two pathsmay be a first path between the UPF network element and a master basestation, and a second path between the UPF network element and asecondary base station. The base station is the master base station. Ina single connectivity scenario, the two paths may be a first path and asecond path between the UPF network element and the base station.

According to the foregoing method, the base station sends the firstaccess network tunnel information and the second access network tunnelinformation to the SMF network element. For a specific first service(for example, a URLLC service requiring high reliability), the SMFnetwork element sends, to the UPF network element, the downlinkforwarding rule including the first access network tunnel informationand the second access network tunnel information such that aftersubsequently receiving a downlink packet of the first service, the UPFnetwork element replicates the downlink packet of the first service, andsends downlink packets of the first service through the two pathsrespectively corresponding to the first access network tunnelinformation and the second access network tunnel information. In thisway, reliability of packet transmission of the first service isimproved.

In a possible design, if the first service is at a service flowgranularity, the downlink forwarding rule further includes a serviceflow identifier of the first service and a session identifier, or if thefirst service is at a session granularity, the downlink forwarding rulefurther includes a session identifier of the first service. Therefore,for services at different granularities, downlink forwarding rules forcorresponding granularities may be provided such that the UPF networkelement can implement more accurate and efficient packet transmission.

In a possible design, the method further includes receiving, by the basestation, indication information from the SMF network element.Correspondingly, the determining, by a base station, first accessnetwork tunnel information and second access network tunnel informationthat correspond to a first service includes determining, by the basestation, the first access network tunnel information and the secondaccess network tunnel information based on the indication information.For example, the indication information may include at least one of thefollowing a QoS parameter, slice identification information, a DN name,and first core network tunnel information and second core network tunnelinformation.

In a possible design, the method further includes receiving, by the basestation, an uplink forwarding rule from the SMF network element, wherethe uplink forwarding rule includes the first core network tunnelinformation and the second core network tunnel information, andreplicating, by the base station, a received uplink packet of the firstservice according to the uplink forwarding rule, and sending uplinkpackets of the first service to the UPF network element through twopaths respectively corresponding to the first core network tunnelinformation and the second core network tunnel information. The basestation herein is a base station in a single connectivity scenario.

Similarly, if the first service is at the service flow granularity, theuplink forwarding rule further includes the service flow identifier ofthe first service and the session identifier, or if the first service isat the session granularity, the uplink forwarding rule further includesthe session identifier of the first service.

In a possible design, the method further includes indicating, by thebase station, UE to add a service flow identifier to a first uplinkpacket.

In a possible design, the method further includes, when the base stationdetermines to transmit a packet in a dual connectivity manner,indicating, by the base station, the UE to generate two second uplinkpackets, where the two second uplink packets have a same sequence numberand a same service flow identifier.

In a possible design, the method further includes indicating, by thebase station, the UE to deduplicate received downlink packets that havea same sequence number and a same service flow identifier. For example,in a dual connectivity (or dual base station) downlink scenario, thebase station indicates the UE to deduplicate received downlink packetsthat have a same sequence number and a same service flow identifier.

In a possible design, the method further includes receiving, by the basestation, the downlink packets of the first service through the two pathsrespectively corresponding to the first access network tunnelinformation and the second access network tunnel information, anddeduplicating downlink packets that have the same sequence number andthe same service flow identifier. For example, in a single connectivity(or single base station) downlink scenario, the base stationdeduplicates downlink packets that have a same sequence number and asame service flow identifier.

In a possible design, the method further includes sending, by the basestation, indication information to the UE using an access stratum (AS)message, where the indication information indicates the UE to replicatean uplink packet to obtain the first uplink packet and the second uplinkpacket, and send the first uplink packet and the second uplink packetover different radio bearers.

According to a third aspect, an embodiment of this application providesa packet transmission method. The method includes obtaining, by a basestation, a first indication, and indicating, according to the firstindication, UE to add a service flow identifier to a first uplinkpacket, where the first indication includes capability information orindication information that is from a session management networkelement. Therefore, for the UE, a same protocol stack format is used fora single connectivity manner and a dual connectivity manner. After theUE is subsequently switched to the dual connectivity manner, the UE maydirectly perform processing based on the protocol stack format, to avoidcomplex operations and signaling exchanges, and reduce a latency,thereby improving user experience.

In a possible design, the indication information indicates the basestation to indicate the UE to add the service flow identifier to anuplink packet of a first session or an uplink packet of a first serviceflow of a first session.

In a possible design, when the first indication includes the capabilityinformation, the indicating, by the base station according to the firstindication, UE to add a service flow identifier to a first uplink packetincludes, when the capability information meets a first condition,indicating, by the base station, the UE to add the service flowidentifier to the first uplink packet, where the first conditionincludes at least one of the following the capability informationindicates that the base station has a capability of transmitting orreceiving a packet in the dual connectivity manner, the capabilityinformation indicates that a neighboring base station of the basestation has the capability of transmitting or receiving a packet in thedual connectivity manner, and the capability information indicates thatanother base station having the capability of transmitting or receivinga packet in the dual connectivity manner is deployed in a sliceassociated with the base station.

In a possible design, the method further includes, when the base stationdetermines to transmit a packet in the dual connectivity manner,indicating, by the base station, the UE to generate two second uplinkpackets, where the two second uplink packets have a same sequence numberand a same service flow identifier.

In a possible design, the method further includes indicating, by thebase station, the UE to deduplicate received downlink packets that havea same sequence number and a same service flow identifier. For example,in a dual connectivity (or dual base station) downlink scenario, thebase station indicates the UE to deduplicate received downlink packetsthat have a same sequence number and a same service flow identifier.

In a possible design, the method further includes receiving, by the basestation, downlink packets of a first service through the two pathsrespectively corresponding to the first access network tunnelinformation and the second access network tunnel information, anddeduplicating downlink packets that have a same sequence number and asame service flow identifier. For example, in a single connectivity (orsingle base station) downlink scenario, the base station deduplicatesdownlink packets that have a same sequence number and a same serviceflow identifier.

According to a fourth aspect, an embodiment of this application providesa packet transmission method. The method includes generating, by UE, afirst uplink packet and a second uplink packet according to anindication obtained from a first base station, where the first uplinkpacket and the second uplink packet have a same first service flowidentifier and a same first sequence number, and sending the firstuplink packet to the first base station, and sending the second uplinkpacket to a second base station. Therefore, for a dual connectivitymanner, the UE adds the service flow identifier and the sequence numberto the uplink packet according to the indication of the base station.For a packet of a specific service (for example, a URLLC servicerequiring high reliability), the UE replicates a packet. In this way,reliability of packet transmission of the specific service is improved.

In a possible design, the method further includes receiving, by the UE,a first downlink packet and a second downlink packet from the first basestation and the second base station respectively, where the firstdownlink packet and the second downlink packet include a same secondservice flow identifier and a same second sequence number, anddeduplicating, by the UE, the first downlink packet and the seconddownlink packet according to the indication of the base station.

According to a fifth aspect, an embodiment of this application providesa packet transmission method. The method includes initiating, by a firstbase station, establishment of a first radio bearer between the firstbase station and UE, and in a process of establishing a second radiobearer between a second base station and the UE, sending, by the firstbase station or the second base station, indication information to theUE, where the indication information indicates the UE to associate thefirst radio bearer and the second radio bearer with a same packet dataconvergence protocol (PDCP) entity on the UE.

In a possible design, the sending, by the first base station or thesecond base station, indication information to the UE includes sending,by the first base station or the second base station, the indicationinformation to the UE using a radio resource control (RRC) layermessage.

According to a sixth aspect, an embodiment of this application providesa packet transmission method. The method includes interacting, by UE,with a first base station, to establish a first radio bearer between thefirst base station and the UE, in a process of establishing a secondradio bearer between a second base station and the UE, receiving, by theUE, indication information from the first base station or the secondbase station, where the indication information indicates the UE toassociate the first radio bearer and the second radio bearer with a samePDCP entity on the UE, generating, by the UE, a first packet and asecond packet based on the indication information, where the firstpacket and the second packet have a same sequence number, and sending,by the UE, the first packet to the first base station over the firstradio bearer, and sending the second packet to the second base stationover the second radio bearer.

In a possible design, the generating, by the UE, a first packet and asecond packet based on the indication information includes replicating,by the UE, a packet at a PDCP layer based on the indication information,to obtain the first packet and the second packet.

According to a seventh aspect, an embodiment of this applicationprovides a packet transmission method. The method includes obtaining, byUE, indication information from a network side device, and generating,by the UE, a first uplink packet and a second uplink packet based on theindication information, sending the first uplink packet to a first basestation over a first radio bearer, and sending the second uplink packetto a second base station over a second radio bearer, where the firstuplink packet and the second uplink packet have a same sequence number.

In a possible design, the first uplink packet corresponds to a firstservice flow identifier, and the second uplink packet corresponds to asecond service flow identifier.

In a possible design, the generating, by the UE, a first uplink packetand a second uplink packet based on the indication information includesreplicating, by the UE, a packet at a first protocol layer based on theindication information, to obtain the first uplink packet and the seconduplink packet. For example, the first protocol layer includes a highreliability protocol (HRP) layer, and the UE obtains the indicationinformation from a SMF network element using a NAS message, or the firstprotocol layer includes a service data adaptation protocol (SDAP) layer,and the UE obtains the indication information from the first basestation using an AS message.

In a possible design, the method further includes receiving, by the UE,a first downlink packet and a second downlink packet from the first basestation and the second base station respectively, where the firstdownlink packet has a second sequence number and corresponds to thefirst service flow identifier, and the second downlink packet has thesecond sequence number and corresponds to the second service flowidentifier, and deduplicating, by the UE, the first downlink packet andthe second downlink packet based on the indication information.

According to an eighth aspect, an embodiment of this applicationprovides a packet transmission method. The method includes receiving, bya UPF network element, an uplink forwarding rule from a SMF networkelement, receiving, by the UPF network element, a first uplink packetand a second uplink packet, where the first uplink packet has a firstservice flow identifier and a first sequence number, and the seconduplink packet has a second service flow identifier and the firstsequence number, and deduplicating, by the UPF network element, thefirst uplink packet and the second uplink packet according to the uplinkforwarding rule.

In a possible design, the uplink forwarding rule indicates the UPFnetwork element to deduplicate the two uplink packets that have the samesequence number and that respectively have the first service flowidentifier and the second service flow identifier.

In a possible design, the method further includes receiving, by the UPFnetwork element, a downlink forwarding rule from the SMF networkelement, and generating, by the UPF network element, a first downlinkpacket and a second downlink packet according to the downlink forwardingrule, sending the first downlink packet to a first base station, andsending the second downlink packet to a second base station, where thefirst downlink packet has the first service flow identifier and a secondsequence number, and the second downlink packet has the second serviceflow identifier and the second sequence number.

In a possible design, the generating, by the UPF network element, afirst downlink packet and a second downlink packet according to thedownlink forwarding rule includes replicating, by the UPF networkelement, a packet at a first protocol layer according to the downlinkforwarding rule, to obtain the first downlink packet and the seconddownlink packet, where the first protocol layer includes a HRP layer ora General Packet Radio Service (GPRS) Tunneling Protocol-user plane(GTP-U) layer.

According to a ninth aspect, an embodiment of this application providesa packet transmission apparatus. The apparatus may be a SMF networkelement or a chip. The apparatus has a function of implementing behaviorof the SMF network element according to the first aspect or the possibledesigns of the first aspect. The function may be implemented byhardware, or may be implemented by hardware executing correspondingsoftware. The hardware or software includes one or more modulescorresponding to the foregoing function. In a possible design, astructure of the apparatus includes a processor and a transceiver. Theprocessor is configured to perform a corresponding function according tothe first aspect or the possible designs of the first aspect. Thetransceiver is configured to implement communication between theapparatus and a UPF network element and between the apparatus and a basestation. The apparatus may further include a memory. The memory isconfigured to couple to the processor, and store a program instructionand data that are necessary for the apparatus.

According to a tenth aspect, an embodiment of this application providesa packet transmission apparatus. The apparatus may be a base station, ormay be a chip. The apparatus has a function of implementing behavior ofthe base station according to the second aspect or the possible designsof the second aspect, or has a function of implementing behavior of thebase station according to the third aspect or the possible designs ofthe third aspect, or has a function of implementing behavior of the basestation according to the fifth aspect or the possible designs of thefifth aspect. The function may be implemented by hardware, or may beimplemented by hardware executing corresponding software. The hardwareor software includes one or more modules corresponding to the foregoingfunction. In a possible design, a structure of the apparatus includes aprocessor and a transceiver. The processor is configured to perform acorresponding function according to the second aspect or the possibledesigns of the second aspect, or perform a corresponding functionaccording to the third aspect or the possible designs of the thirdaspect, or perform a corresponding function according to the fifthaspect or the possible designs of the fifth aspect. The transceiver isconfigured to implement communication between the apparatus and a SMFnetwork element and between the apparatus and a UPF network element. Theapparatus may further include a memory. The memory is configured tocouple to the processor, and store a program instruction and data thatare necessary for the apparatus.

According to an eleventh aspect, an embodiment of this applicationprovides a packet transmission apparatus. The apparatus may be UE, ormay be a chip. The apparatus has a function of implementing behavior ofthe UE according to the fourth aspect or the possible designs of thefourth aspect, or has a function of implementing behavior of the UEaccording to the sixth aspect or the possible designs of the sixthaspect, or has a function of implementing behavior of the base stationaccording to the seventh aspect or the possible designs of the seventhaspect. The function may be implemented by hardware, or may beimplemented by hardware executing corresponding software. The hardwareor software includes one or more modules corresponding to the foregoingfunction. In a possible design, a structure of the apparatus includes aprocessor and a transceiver. The processor is configured to perform acorresponding function according to the fourth aspect or the possibledesigns of the fourth aspect, or perform a corresponding functionaccording to the sixth aspect or the possible designs of the sixthaspect, or perform a corresponding function according to the seventhaspect or the possible designs of the seventh aspect. The transceiver isconfigured to implement communication between the apparatus and a basestation and between the apparatus and a SMF network element. Theapparatus may further include a memory. The memory is configured tocouple to the processor, and store a program instruction and data thatare necessary for the apparatus.

According to a twelfth aspect, an embodiment of this applicationprovides a packet transmission apparatus. The apparatus may be a UPFnetwork element or a chip. The apparatus has a function of implementingbehavior of the UPF network element according to the eighth aspect orthe possible designs of the eighth aspect. The function may beimplemented by hardware, or may be implemented by hardware executingcorresponding software. The hardware or software includes one or moremodules corresponding to the foregoing function. In a possible design, astructure of the apparatus includes a processor and a transceiver. Theprocessor is configured to perform a corresponding function according tothe eighth aspect or the possible designs of the eighth aspect. Thetransceiver is configured to implement communication between theapparatus and a SMF network element and between the apparatus and a basestation. The apparatus may further include a memory. The memory isconfigured to couple to the processor, and store a program instructionand data that are necessary for the apparatus.

According to a thirteenth aspect, an embodiment of this applicationprovides a packet transmission system. The system includes a SMF networkelement configured to perform the method according to the first aspector the possible designs of the first aspect, and a base stationconfigured to perform the method according to the second aspect or thepossible designs of the second aspect. In a dual connectivity scenario,the base station that performs the method according to the second aspector the possible designs of the second aspect is a master base station.Optionally, the system may further include a secondary base stationconfigured to implement dual connectivities.

According to a fourteenth aspect, an embodiment of this applicationfurther provides a computer-readable storage medium. Thecomputer-readable storage medium stores an instruction, and when theinstruction is run on a computer, the computer is enabled to perform themethods according to the foregoing aspects.

According to a fifteenth aspect, an embodiment of this applicationprovides a computer program product including an instruction. When thecomputer program product is run on a computer, the computer is enabledto perform the methods according to the foregoing aspects.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of dual transmission paths in a 5G dualconnectivity mechanism.

FIG. 2 is a schematic diagram of dual connectivities in a 5Gcommunications system.

FIG. 3A and FIG. 3B are a signaling exchange diagram of a packettransmission method according to an embodiment of this application.

FIG. 4 is a schematic diagram of a single connectivity in a 5Gcommunications system.

FIG. 5 is a signaling exchange diagram of a packet transmission methodaccording to another embodiment of this application.

FIG. 6 is a flowchart of a packet transmission method according to anembodiment of this application.

FIG. 7 is another flowchart of a packet transmission method according toan embodiment of this application.

FIG. 8 is a schematic structural diagram of a packet transmissionapparatus according to an embodiment of this application.

FIG. 9 is a schematic structural diagram of another packet transmissionapparatus according to an embodiment of this application.

FIG. 10 is another schematic structural diagram of a packet transmissionapparatus according to an embodiment of this application.

FIG. 11A and FIG. 11B are a signaling exchange diagram of a packettransmission method according to another embodiment of this application.

FIG. 12A and FIG. 12B are a signaling exchange diagram of a packettransmission method according to another embodiment of this application.

FIG. 13 is a flowchart of a packet transmission method according toanother embodiment of this application.

FIG. 14 is a flowchart of a packet transmission method according toanother embodiment of this application.

FIG. 15A and FIG. 15B are a signaling exchange diagram of a packettransmission method according to another embodiment of this application,where the method is applicable to a solution for enhancing a PDCP layer.

FIG. 16 is a flowchart of a packet transmission method on a base stationside according to another embodiment of this application.

FIG. 17 is a flowchart of a packet transmission method on a UE sideaccording to another embodiment of this application.

FIG. 18A and FIG. 18B are a signaling exchange diagram of a packettransmission method according to another embodiment of this application,where the method is applicable to a solution for an HRP layer.

FIG. 19A and FIG. 19B are a signaling exchange diagram of a packettransmission method according to another embodiment of this application,where the method is applicable to a solution for an SDAP layer.

FIG. 20 is a flowchart of a packet transmission method on a UE sideaccording to another embodiment of this application.

FIG. 21 is a flowchart of a packet transmission method on a UPF sideaccording to another embodiment of this application.

DESCRIPTION OF EMBODIMENTS

The following clearly describes the technical solutions in theembodiments of this application with reference to the accompanyingdrawings in the embodiments of this application.

In a 5G mobile network architecture, a core network includes a controlplane (CP) network element and a user plane network element. The CPnetwork element is a unified CP that integrates a conventional 3rdGeneration Partnership Project (3GPP) control network element mobilitymanagement entity (MME), a CP function of a serving gateway (SGW), a CPfunction of a packet data network gateway (PGW), and the like. The UPFnetwork element can implement a UPF of the SGW (SGW-U) and a UPF of thePGW (PGW-U). Further, the unified CP network element may be decomposedinto an access and mobility management function (AMF) network elementand a SMF network element.

FIG. 2 is a schematic diagram of a 5G communications system according toan embodiment of this application. As shown in FIG. 2, thecommunications system includes at least UE 201, a RAN device (forexample, an M-RAN device 202 and an S-RAN device 203), an AMF networkelement 204, an SMF network element 205, and a UPF network element 206.

The UE 201 in this system is not limited to being in a 5G network, andincludes a mobile phone, an internet of things device, a smart homedevice, an industrial control device, a vehicle device, and the like.The UE may also be referred to as a terminal, a terminal device, amobile station, a remote station, a remote terminal, an access terminal,a user terminal, or a user agent. This is not limited herein. The UE mayalternatively be a vehicle in vehicle-to-vehicle (V2V) communication, amachine in machine type communication, or the like.

The RAN device is an apparatus configured to provide a wirelesscommunication function for the UE 201. The M-RAN device 202 is used asan example. The M-RAN device 202 may include base stations in variousforms, for example, a macro base station, a micro base station (alsoreferred to as a small cell), a relay station, or an access point. Insystems using different radio access technologies, names of deviceshaving a base station function may be different. For example, in a thirdgeneration (3G) system, the device is referred to as a NodeB. In aLong-Term Evolution (LTE) system, the device is referred to as anevolved NodeB (eNB). In a 5G system, the device is referred to as agNodeB (gNB). The M-RAN device 202 is referred to as an M-RAN 202 forshort below. The S-RAN device 203 is similar to the M-RAN device 202,and details are not described again.

The AMF network element 204 may be responsible for registration,mobility management, a tracking area update procedure, and the like ofthe UE 201. The AMF network element 204 is referred to as an AMF 204 forshort below.

The SMF network element 205 may be responsible for session management ofthe UE 201. For example, the session management includes establishment,modification, and release of a session, UPF network element selectionand reselection, and internet protocol (IP) address assignment. The SMFnetwork element 205 is referred to as an SMF 205 for short below.

The UPF network element 206 may be connected to a DN 207, and isconfigured to transmit a data packet of a service. The UPF networkelement 206 is referred to as a UPF 206 for short below.

In a dual connectivity mechanism, there are two paths for transmittingan uplink packet/a downlink packet one path passes through (1) the UE201, the M-RAN 202, the UPF 206, and the DN 207, and the other pathpasses through (2) the UE 201, the S-RAN 203, the UPF 206, and the DN207. There is a signaling connection between the M-RAN 202 and the S-RAN203, and there is a signaling connection between the M-RAN 202 and a CPnetwork element, such as the AMF 204 or the SMF 205. Optionally, thereis no signaling connection between the S-RAN and the CP.

The foregoing network elements may also be referred to as devices orentities. For example, the AMF network element may also be referred toas an AMF device or an AMF entity.

The foregoing network elements may be implemented by specified hardware,or may be implemented by a software instance on specified hardware, ormay be implemented by a virtual function instantiated on an appropriateplatform. This is not limited in the present disclosure.

Optionally, the communications system is applicable to a serviceframework. In the service framework, a service-based interface is usedon a CP. For example, the AMF network element 204 and the SMF networkelement 204 respectively have a service-based interface Namf and aservice-based interface Nsmf. One function network element may exposeits capability to another authorized function network element through aservice-based interface, to provide a network function (NF) service. Inother words, the NF service refers to various capabilities that can beprovided.

In addition, this embodiment of this application is further applicableto another future-oriented communications technology. The networkarchitecture and the service scenario described in this application areintended to describe the technical solutions in this application moreclearly, and do not constitute a limitation on the technical solutionsprovided in this application. A person of ordinary skill in the art mayknow that with evolution of the network architecture and emergence of anew service scenario, the technical solutions provided in thisapplication are also applicable to similar technical problems.

The 3GPP defines three main 5G scenarios enhanced mobile broadband(eMBB), massive machine-type communications (mMTC), and URLLC. Featuresof the URLLC include high reliability and a low latency, and the URLLCmay be applied to unmanned driving, industrial automation, remotemanufacturing, remote training, remote surgery, and the like. Forexample, for the URLLC, a desired uplink user plane latency is 0.5milliseconds (ms), and a desired downlink user plane latency is 0.5 ms.An objective of reliability is that a packet loss rate for a 32-bytepacket does not exceed 1 to 10{circumflex over ( )}(−5) within a userplane latency of 1 ms.

This application is intended to provide a packet transmission solutionhaving high reliability. For example, the packet transmission solutionmay be applied to a URLLC scenario.

FIG. 3A and FIG. 3B are a signaling exchange diagram of a packettransmission method according to an embodiment of this application. FIG.3A and FIG. 3B relate to interaction between UE, a master base station,a secondary base station, an AMF, an SMF, and a UPF. For example, theUE, the master base station, the secondary base station, the AMF, theSMF, and the UPF may be respectively the UE 201, the M-RAN 202, theS-RAN 203, the AMF 204, the SMF 205, and the UPF 206 in FIG. 2.

As shown in FIG. 3A and FIG. 3B, the method includes the followingsteps.

Step 301. The UE sends, to the AMF via the master base station, a NASmessage that carries a session establishment request, to request toestablish a packet data unit (PDU) session for the UE.

The NAS message may further include a PDU session identifier (ID),single network slice selection assistance information (S-NSSAI), and aDN name (DNN) that are allocated by the UE to the session. The S-NSSAIindicates a slice type corresponding to the session. The DNN indicates aDN corresponding to the session.

Step 302. Other steps of a session establishment procedure areperformed.

For example, the foregoing other steps include at least the AMF selectsthe SMF, and the SMF selects the UPF. Details are not described herein.

Step 303. The SMF transmits N2 session management (SM) information tothe AMF.

For example, the SMF sends the N2 SM information to the AMF to invoke anN1N2 message transfer service (Namf_Communication_N1N2MessageTransfer)of the AMF. The N2 SM information includes at least the PDU sessionidentifier and core network tunnel information. The N2 SM informationmay further include a QoS parameter, a QoS flow identifier (QFI), sliceidentification information (for example, the S-NSSAI), asession-aggregate maximum bit rate (session-AMBR), and a PDU sessiontype. Optionally, the N2 SM information may further include the DNN. Inaddition, an N1 SM container including a session accept message mayfurther be sent to the AMF by invoking the service.

Step 304. The AMF sends the N2 SM information to the master basestation.

For example, the AMF sends an N2 session request to the master basestation, and the N2 session request includes the N2 SM information and aNAS message. The NAS message includes the PDU session identifier and theN1 SM container.

The core network tunnel information includes first core network tunnelinformation and second core network tunnel information. The first corenetwork tunnel information and the second core network tunnelinformation may be allocated by the SMF and sent to the master basestation by being forwarded by the AMF, or may be allocated by the UPFand sent to the SMF, and then sent by the SMF to the master base stationby being forwarded by the AMF.

For example, the first core network tunnel information includes a firstIP address of the UPF and a first tunnel endpoint identifier (TEID) ofthe UPF. The second core network tunnel information includes a second IPaddress of the UPF and a second TEID of the UPF. The first IP addressand the second IP address may be the same or may be different. The firstTEID and the second TEID are different.

When the first IP address and the second IP address are different, thefirst IP address and the second IP address may identify two paths thatare independent of each other. The two paths that are independent ofeach other are two paths that pass through different transmissionentities (such as a switch and a router). Details are not describedbelow again.

When the first IP address and the second IP address are the same, the N2SM information further includes first network identification informationcorresponding to the first TEID and second network identificationinformation corresponding to the second TEID. The first networkidentification information and the second network identificationinformation identify two paths that are independent of each other. Thefirst network identification information is as an example. The firstTEID and the first network identification information may be allocatedby different network elements. The first network identificationinformation may include a virtual local area network (VLAN) ID or amulti-protocol label switching (MPLS) label. For example, the networkidentification information corresponding to the first TEID is a VLAN ID1, and the network identification information corresponding to thesecond TEID is a VLAN ID 2. In this way, when the first IP address andthe second IP address are the same, when the first core network tunnelinformation and the second core network tunnel information aresubsequently sent, the first network identification informationcorresponding to the first TEID and the second network identificationinformation corresponding to the second TEID are also sent. Details arenot described below again. For example, the first core network tunnelinformation and the first network identification information may be sentusing a first container, and the second core network tunnel informationand the second network identification information may be sent using asecond container.

Step 305. The master base station initiates establishment of an accessnetwork resource between the master base station and the UE.

Step 306. The master base station determines to add the secondary basestation, and sends a secondary base station adding request to thesecondary base station.

The master base station may determine, based on indication information,to transmit an uplink packet of a first service through dual paths, todetermine that the secondary base station needs to be added. The firstservice includes a URLLC service. For example, any one or a combinationof the QoS parameter, the slice identification information, the DNN, andthe first core network tunnel information and the second core networktunnel information that are included in the N2 SM information may beused as the indication information. The QoS parameter includes at leastone of a 5G QoS identifier (5QI) and a QFI. For example, if the masterbase station determines, based on the QoS parameter in the N2 SMinformation, that the session requires high reliability, the master basestation determines to add the secondary base station, or if the masterbase station determines, based on the slice identification informationin the N2 SM information, that the session is associated with a slice inURLLC, the master base station determines to add the secondary basestation, or if the master base station determines, based on the DNN inthe N2 SM information, that the session is associated with a DN inURLLC, the master base station determines to add the secondary basestation, or if the master base station directly determines, based on thefirst core network tunnel information and the second core network tunnelinformation in the N2 SM information, to transmit the uplink packetthrough the dual paths, the master base station determines to add thesecondary base station. Because first access network tunnel informationand second access network tunnel information need to be used fortransmission of the downlink packet through the dual paths, it may alsobe considered that the indication information triggers determining ofthe first access network tunnel information and the second accessnetwork tunnel information. The first access network tunnel informationmay be determined by the master base station, and the second accessnetwork tunnel information may be determined by the secondary basestation and sent to the master base station.

For example, the first access network tunnel information includes athird IP address of the master base station and a third TEID of themaster base station, and the second access network tunnel informationincludes a fourth IP address of the secondary base station and a fourthTEID of the secondary base station.

Optionally, if the master base station finds that the downlink packet ofthe first service cannot be transmitted through the dual paths in acurrent environment (as described in a measurement report reported bythe UE), the master base station feeds back indication information tothe AMF, and the AMF sends the indication information to the SMF, wherethe indication information indicates that the downlink packet of thefirst service cannot be transmitted through the dual paths. Afterreceiving the indication information, the SMF rejects the sessionestablishment procedure or performs a subsequent step in a sessionestablishment procedure in other approaches.

Step 307. The secondary base station returns a secondary base stationadding request acknowledgment to the master base station.

For example, the secondary base station adding request acknowledgmentincludes the second access network tunnel information determined by thesecondary base station.

Optionally, if the first service is at a session granularity, thesecondary base station adding request sent in step 306 includes asession identifier of the first service. Therefore, the second accessnetwork tunnel information determined by the secondary base station isalso at the session granularity and corresponds to the sessionidentifier. If the first service is at a service flow granularity, thesecondary base station adding request sent in step 306 includes a QFI ofa service flow of the first service. Therefore, the second accessnetwork tunnel information determined by the secondary base station isalso at the service flow granularity and corresponds to the QFI. From aperspective of a protocol stack, if the master base station determinesto add the secondary base station, the master base station generates aPDCP entity for the QFI, and after receiving the secondary base stationadding request, the secondary base station generates a PDCP entity forthe QFI. In this way, the QFI is associated with the two PDCP entities.Therefore, that the master base station determines to add the secondarybase station, in an embodiment, transmits a packet in a dualconnectivity manner, may also be understood as that the QFI isassociated with the two PDCP entities.

As described above, the first access network tunnel information includesthe third IP address of the master base station and the third TEID ofthe master base station, and the second access network tunnelinformation includes the fourth IP address of the secondary base stationand the fourth TEID of the secondary base station. The third IP addressand the fourth IP address may be the same or may be different. The thirdTEID and the fourth TEID are different.

When the third IP address and the fourth IP address are different, thethird IP address and the fourth IP address identify two paths that areindependent of each other.

When the third IP address and the fourth IP address are the same, afterreceiving the second access network tunnel information, the master basestation allocates third network identification information correspondingto the third TEID and fourth network identification informationcorresponding to the fourth TEID. The third network identificationinformation and the fourth network identification information identifytwo paths that are independent of each other. For the third/fourthnetwork identification information, refer to the descriptions of thefirst network identification information. Details are not describedherein again. In this way, when the third IP address and the fourth IPaddress are the same, when subsequently sending the first access networktunnel information and the second access network tunnel information, themaster base station further sends the third network identificationinformation corresponding to the third TEID, and sends the fourthnetwork identification information corresponding to the fourth TEID.Details are not described below again. For example, the master basestation may send the first access network tunnel information and thethird network identification information using a third container, andsend the second access network tunnel information and the fourth networkidentification information using a fourth container.

Step 308. The master base station initiates RRC connectionreconfiguration to the UE.

Step 309. The master base station feeds back secondary base stationreconfiguration completion to the secondary base station, to notify thesecondary base station that the UE successfully completes the RRCconnection reconfiguration.

Optionally, if the secondary base station has an RRC function, theforegoing step 307 to step 309 may be replaced with the following steps.

307′. The secondary base station initiates an RRC connectionestablishment process to the UE.

308′. The secondary base station returns a secondary base station addingrequest acknowledgment to the master base station. For details, refer tothe descriptions of step 307. Details are not described again.

Step 310. Random access procedure is performed.

It should be noted that, a sequence of step 308, step 309, and step 310is not limited herein, or the random access procedure may be firstperformed, and then step 308 and step 309 are performed.

Optionally, in another embodiment, the master base station maydetermine, before step 305, whether the secondary base station needs tobe added. For how the master base station determines whether thesecondary base station needs to be added, refer to the descriptions ofstep 306. Details are not described herein again. If the master basestation determines to add the secondary base station (in an embodiment,transmit a packet in the dual connectivity manner), the master basestation may indicate, through step 305 or step 308, the UE to add aservice flow identifier and a sequence number to an uplink packet(replicate the uplink packet, where the replicated uplink packets havethe same service flow identifier and the same sequence number). If themaster base station determines not to add the secondary base station (inan embodiment, transmit a packet in a single connectivity manner), themaster base station further determines whether obtained capabilityinformation meets a first condition. When the capability informationmeets the first condition, the master base station may indicate, throughstep 305 or step 308, the UE to add a service flow identifier to anuplink packet.

For example, the capability information indicates at least one of thefollowing, whether the base station (namely, the master base station)has a capability of transmitting or receiving a packet in the dualconnectivity manner, whether a neighboring base station (namely, a basestation, for example, the secondary base station, having an Xn interfacewith the base station) of the base station has the capability oftransmitting or receiving a packet in the dual connectivity manner, andwhether another base station (for example, the secondary base station)that has the capability of transmitting or receiving a packet in thedual connectivity manner is deployed in a slice associated with the basestation.

For example, the master base station may obtain the capabilityinformation through configuration, in an Xn connection establishmentprocess between the master base station and the neighboring basestation, or in an N2 session establishment process. For example, in theXn connection establishment process between the base station and theneighboring base station, the neighboring base station sends capabilityinformation of the neighboring base station to the base station. In theN2 session establishment process between the base station and the AMF,the SMF sends a deployment status in the slice to the base station inthe N2 session establishment process.

In addition, the base station may determine, using allowed network sliceselection assistance information (NSSAI) returned by the AMF in aregistration procedure, the slice associated with the base station, orthe base station may determine, based on S-NSSAI that corresponds to asession and that is returned by the SMF in the session establishmentprocess, the slice associated with the base station. Therefore, the basestation may determine, with reference to the obtained base stationdeployment status in the slice, whether another base station having thecapability of transmitting or receiving a packet in the dualconnectivity manner is deployed in the slice associated with the basestation.

The first condition includes at least one of the following. The basestation (namely, the master base station) has the capability oftransmitting or receiving a packet in the dual connectivity manner, theneighboring base station (namely, the secondary base station) of thebase station has the capability of transmitting or receiving a packet inthe dual connectivity manner, and the other base station (for example,the secondary base station) that has the capability of transmitting orreceiving a packet in the dual connectivity manner is deployed in theslice associated with the master base station.

In other words, the capability information meets the first conditionwhen the capability information indicates at least one of the followingindicating that the base station has the capability of transmitting orreceiving a packet in the dual connectivity manner, indicating that theneighboring base station (for example, the secondary base station) ofthe base station has the capability of transmitting or receiving apacket in the dual connectivity manner, and indicating that the otherbase station (for example, the secondary base station) that has thecapability of transmitting or receiving a packet in the dualconnectivity manner is deployed in the slice associated with the basestation. It may be understood that when the capability information meetsthe first condition, it indicates that the UE has a possibility oftransmitting or receiving a packet in the dual connectivity manner. Evenif the UE currently uses the single connectivity manner, the UE may besubsequently switched to the dual connectivity manner.

Therefore, when the dual connectivity manner is used or the dualconnectivity manner may be used subsequently, the base station indicatesthe UE to add the service flow identifier to the uplink packet. Forexample, the base station may indicate the UE to enable the SDAP, toindicate the UE to add the service flow identifier to the uplink packet.The service flow identifier may be included in an SDAP header. That theUE enables the SDAP means that the UE adds the SDAP header to the uplinkpacket.

The service flow identifier may include at least one of a sessionidentifier, a QFI, and a 5-tuple.

Therefore, if the dual connectivity manner may be used subsequently,even currently single connectivity is used, the base station alsoindicates the UE to add the service flow identifier. In this way, forthe UE, a same protocol stack format is used for the single connectivitymanner and the dual connectivity manner. After the UE is subsequentlyswitched to the dual connectivity manner, the UE may directly performprocessing based on the protocol stack format, to avoid complexoperations and signaling exchanges, and reduce a latency, therebyimproving user experience.

However, in the dual connectivity manner, because the UE needs toreplicate the uplink packet, the master base station indicates the UE toadd the sequence number. It may be understood that the UE may processthe uplink packet in various manners, and a plurality of processeduplink packets have a same sequence number. For example, the UE mayfirst add a sequence number to a first uplink packet, and then replicatethe first uplink packet to which the sequence number is added, to obtaina second uplink packet having the same sequence number, or the UE mayfirst replicate a first uplink packet to obtain a second uplink packet,and then add a same sequence number to the first uplink packet and thesecond uplink packet. This is not limited in this application.

Optionally, the base station further indicates the UE to deduplicatereceived downlink packets that have a same sequence number and a sameservice flow identifier.

Optionally, in another embodiment, the base station (namely, the masterbase station) may determine, before step 305, whether the obtainedcapability information meets the first condition. When the capabilityinformation meets the first condition, the UE may be indicated, throughstep 305, to add the service flow identifier to the uplink packet. Ifthe master base station determines, in step 306, that the secondary basestation needs to be added, the master base station may indicate, throughstep 308, the UE to add the sequence number to the uplink packet. Forhow to determine whether the capability information meets the firstcondition, how to determine whether the secondary base station needs tobe added, how to indicate the UE to add the service flow identifier tothe uplink packet, and how to indicate the UE to add the sequence numberto the uplink packet, refer to the foregoing descriptions. Details arenot described herein again.

Optionally, the base station further indicates the UE to deduplicatereceived downlink packets that have a same sequence number and a sameservice flow identifier.

Optionally, in still another embodiment, the N2 SM informationtransmitted in step 303 and step 304 further includes indicationinformation, and the indication information indicates the base station(namely, the master base station) to indicate the UE to add the serviceflow identifier to an uplink packet of a first session or an uplinkpacket of a first service flow of a first session. That is, the SMF maydetermine whether the UE needs to add the service flow identifier to theuplink packet. For example, when the SMF determines, based on the QFI inthe N2 SM information sent by the UE to the SMF, that the sessionrequires high reliability, and/or determines, based on the sliceidentification information in the N2 SM information, that the session isassociated with a slice in URLLC, and/or determines, based on the DNN inthe N2 SM information, that the session is associated with a DN inURLLC, and/or determines, based on subscription data of the UE, that theUE is UE in URLLC, the SMF determines that the UE needs to add theservice flow identifier to the uplink packet, and therefore sends theindication information to the base station, and after the base stationreceives the indication information, the base station indicates the UEto add the service flow identifier to the uplink packet. In this way,the base station may not perform determining, thereby simplifying anoperation on a base station side.

Optionally, the base station further indicates the UE to deduplicatereceived downlink packets that have a same sequence number and a sameservice flow identifier.

Step 311. The master base station sends the first access network tunnelinformation and the second access network tunnel information to the AMF.

For example, the master base station returns an N2 session response tothe AMF. The N2 session response includes the PDU session identifier andthe N2 SM information. The N2 SM information includes the first accessnetwork tunnel information and the second access network tunnelinformation. Optionally, when the first service is at the sessiongranularity, the N2 SM information may further include the sessionidentifier corresponding to the first service, or when the first serviceis at the service flow granularity, the N2 SM information may furtherinclude the session identifier and the QFI that correspond to the firstservice.

Step 312. The AMF sends a context update request to the SMF.

For example, the AMF sends an Nsmf_PDUSession_UpdateSMContext request toinvoke an SM context update service (Nsmf_PDUSession_UpdateSMContext) ofthe SMF. The AMF forwards, to the SMF using the request, the N2 SMinformation received in step 311.

Step 313. The SMF sends a downlink forwarding rule to the UPF.

For example, the SMF sends an N4 session modification request to theUPF, and the session modification request includes the downlinkforwarding rule. The UPF returns an N4 session modification response.

It should be noted that, in another implementation, the core networktunnel information in step 303 may include only the first core networktunnel information, but the first access network tunnel information andthe second access network tunnel information are included in step 311.After receiving the first access network tunnel information and thesecond access network tunnel information, the SMF allocates the secondcore network tunnel information, sends the second core network tunnelinformation to the UPF in step 313, and sends the second core networktunnel information to the master base station via the AMF, or afterreceiving the first access network tunnel information and the secondaccess network tunnel information from the SMF, the UPF allocates thesecond core network tunnel information, and returns the second corenetwork tunnel information to the SMF using the N4 session modificationresponse. The SMF sends the second core network tunnel information tothe master base station via the AMF. The master base station sends thesecond core network tunnel information to the secondary base station.

The downlink forwarding rule includes the first access network tunnelinformation and the second access network tunnel information. Thedownlink forwarding rule indicates the UPF to replicate a receiveddownlink packet of the first service (add a flow identifier and asequence number to the downlink packet), and send downlink packets ofthe first service through the two paths corresponding to the firstaccess network tunnel information and the second access network tunnelinformation, separately, in an embodiment, send one downlink packet ofthe first service to the master base station through a first pathcorresponding to the first access network tunnel information, and sendanother downlink packet of the first service to the secondary basestation through a second path corresponding to the second access networktunnel information. The downlink forwarding rule further indicates theUPF to deduplicate received uplink packets that have a same flowidentifier and a same sequence number.

Optionally, when the first service is at the session granularity, the N2SM information received by the SMF in step 312 further includes thesession identifier corresponding to the first service. Therefore, thedownlink forwarding rule further includes the session identifiercorresponding to the first service. When the first service is at theservice flow granularity, the N2 SM information received by the SMF instep 312 further includes the session identifier and the QFI thatcorrespond to the first service. Therefore, the downlink forwarding rulefurther includes the session identifier and the QFI that correspond tothe first service.

Optionally, the session identifier corresponding to the first service inthe N2 SM information received in step 312 and the session identifiercorresponding to the first service in the downlink forwarding rule maybe different, but are associated with each other. For example, thesession identifier corresponding to the first service in the N2 SMinformation received in step 312 is the PDU session identifier. The SMFconverts the PDU session identifier into an N4 session identifier, usesthe N4 session identifier as the session identifier corresponding to thefirst service in the downlink forwarding rule, and sends the N4 sessionidentifier to the UPF.

In addition, the downlink forwarding rule further includes informationabout the first service.

For example, the information about the first service includes at least a5-tuple of the first service. For example, the information about thefirst service may indicate IP addresses of which packets correspond tothe packet of the first service. In other words, the information aboutthe first service functions as a packet filter configured to obtain thepacket of the first service through filtering. For example, the SMF mayobtain the information about the first service from a policy controlfunction (PCF) network element, or locally configure the informationabout the first service.

Step 314. The SMF sends a context update response to the AMF.

Then, after receiving the downlink packet of the first service, the UPFsends the downlink packets of the first service to the master basestation and the secondary base station according to the forwarding rulethrough the first path corresponding to the first access network tunnelinformation and the second path corresponding to the second accessnetwork tunnel information separately. That the downlink packets of thefirst service are transmitted through the two paths also means that thedownlink packets sent through the two paths are the same.

For example, after receiving a downlink packet, the UPF matches a packetheader characteristic of the downlink packet with the information aboutthe first service in the forwarding rule, to determine that the downlinkpacket is a packet of the first service.

After determining that the downlink packet is the packet of the firstservice, the UPF may replicate the packet. In a possible implementation,the UPF sends an original packet to the UE through the first path thatis between the UPF and the master base station and that corresponds tothe first access network tunnel information, and sends a replicatedpacket to the UE through the second path that is between the UPF and thesecondary base station and that corresponds to the second access networktunnel information. In another possible implementation, the UPF sends areplicated packet to the UE through the first path that is between theUPF and the master base station and that corresponds to the first accessnetwork tunnel information, and sends an original packet to the UEthrough the second path that is between the UPF and the secondary basestation and that corresponds to the second access network tunnelinformation. In still another possible implementation, the UPF performspacket replication to obtain two packets, and sends the replicatedpackets to the UE through the first path that is between the UPF and themaster base station and that corresponds to the first access networktunnel information and through the second path that is between the UPFand the secondary base station and that corresponds to the second accessnetwork tunnel information, respectively. In the foregoing severalmanners, the downlink packets transmitted through the dual paths are thesame.

In addition, in an uplink direction, after receiving the first corenetwork tunnel information and the second core network tunnelinformation that are included in the N2 SM information in step 304, themaster base station learns that the UE may subsequently transmit anuplink packet of the first service through the two paths respectivelycorresponding to the first core network tunnel information and thesecond core network tunnel information. For example, the master basestation corresponds to a first path corresponding to the first corenetwork tunnel information, and the secondary base station correspondsto a second path corresponding to the second core network tunnelinformation. Therefore, the master base station may send the second corenetwork tunnel information to the secondary base station using thesecondary base station adding request in step 306. In step 308, afterreceiving the second access network tunnel information determined by thesecondary base station, the master base station sends an uplinkforwarding rule to the UE in the RRC connection reconfiguration process.The uplink forwarding rule includes the first access network tunnelinformation and the second access network tunnel information, and theuplink forwarding rule indicates the UE to replicate a received uplinkpacket of the first service, and send uplink packets of the firstservice to the master base station through the path corresponding to thefirst access network tunnel information, and sends the information tothe secondary base station through the path corresponding to the secondaccess network tunnel information.

Similarly, the uplink forwarding rule further includes the informationabout the first service. Details are not described herein again. Afterdetermining, based on the information about the first service, that anuplink packet is a packet of the first service, the UE may replicate thepacket. In a possible implementation, the UE sends an original packet tothe master base station through the first path corresponding to thefirst access network tunnel information, and sends a replicated packetto the secondary base station through the second path corresponding tothe second access network tunnel information. In another possibleimplementation, the UE sends a replicated packet to the master basestation through the first path corresponding to the first access networktunnel information, and sends an original packet to the secondary basestation through the second path corresponding to the second accessnetwork tunnel information. In still another possible implementation,the UE performs packet replication to obtain two packets, sends one ofthe replicated packets to the master base station through the first pathcorresponding to the first access network tunnel information, and sendsthe other one of the replicated packets to the secondary base stationthrough the second path corresponding to the second access networktunnel information. In the foregoing several manners, the uplink packetstransmitted through the dual paths are the same. After receiving theuplink packet, the master base station sends the uplink packet to theUPF based on the first core network tunnel information. After receivingthe uplink packet, the secondary base station sends the uplink packet tothe UPF based on the second core network tunnel information.

Therefore, according to the packet transmission method in thisembodiment of the present disclosure, the uplink/downlink packets of thefirst service (for example, the URLLC service) may be transmittedthrough the two paths. Similarly, the method in this embodiment of thisapplication may further be used to transmit an uplink packet/a downlinkpacket of the first service through a plurality of (more than two)paths. Details are not described again. Therefore, reliability of packettransmission of the URLLC service is improved.

In addition, the packet transmission solution in this application isalso applicable to a single connectivity (or referred to as single basestation) scenario, as shown in FIG. 4. In this scenario, there are atleast two transmission paths between the RAN 202′ and the UPF 206.

FIG. 5 is a signaling exchange diagram of a packet transmission methodaccording to another embodiment of this application. FIG. 5 relates tointeraction between UE, a base station, an AMF, an SMF, and a UPF. Forexample, the UE, the base station, the AMF, the SMF, and the UPF may berespectively the UE 201, the RAN 202′, the AMF 204, the SMF 205, and theUPF 206 in FIG. 4.

As shown in FIG. 5, the method includes the following steps.

Step 501. The UE sends, to the AMF via the base station, a NAS messagethat carries a session establishment request, to request to establish aPDU session for the UE.

Step 502. Other steps of a session establishment procedure areperformed.

Step 503. The SMF transmits N2 SM information to the AMF.

Step 504. The AMF sends the N2 SM information to the base station.

Step 505. The base station initiates establishment of an access networkresource between the base station and the UE.

For step 501 to step 505, refer to the descriptions of step 301 to step305 in FIG. 3A and FIG. 3B. Details are not described herein again. Thebase station in FIG. 5 may perform the steps of the method performed bythe master base station in FIG. 3A and FIG. 3B.

Similarly, when the base station receives indication information fromthe SMF, or determines that capability information meets a firstcondition, the base station may indicate, through step 505, the UE toadd a service flow identifier. Refer to the descriptions of FIG. 3A andFIG. 3B herein, and details are not described herein again.

Step 506. The base station determines first access network tunnelinformation and second access network tunnel information.

The base station may determine, based on the indication information, totransmit an uplink packet of a first service through dual paths, todetermine that the two pieces of access network tunnel information needto be determined. The first service includes a URLLC service. Forexample, any one or a combination of the QoS parameter, the sliceidentification information, the DNN, and the first core network tunnelinformation and the second core network tunnel information that areincluded in the N2 SM information transmitted in the foregoing step 503and step 504 may be used as the indication information. The QoSparameter includes at least one of a 5QI and a QFI. For example, if thebase station determines, based on the QoS parameter in the N2 SMinformation, that the session requires high reliability, or determines,based on the slice identification information in the N2 SM information,that the session is associated with a slice in URLLC, or if the basestation determines, based on the DNN in the N2 SM information, that thesession is associated with a DN in URLLC, or directly determines, basedon the first core network tunnel information and the second core networktunnel information in the N2 SM information, to transmit the uplinkpacket through the dual paths, the base station determines that the twopieces of access network tunnel information need to be determined.Because the first access network tunnel information and the secondaccess network tunnel information need to be used for transmission ofthe downlink packet through the dual paths, it may further be consideredthat the indication information triggers determining of the first accessnetwork tunnel information and the second access network tunnelinformation.

Optionally, if the base station finds that the downlink packet of thefirst service cannot be transmitted through the dual paths in a currentenvironment, the base station feeds back indication information to theAMF, and the AMF sends the indication information to the SMF, where theindication information indicates that the downlink packet of the firstservice cannot be transmitted through the dual paths. After receivingthe indication information, the SMF rejects the session establishmentprocedure or performs a subsequent step in a session establishmentprocedure in other approaches.

Similarly, the first access network tunnel information includes a thirdIP address and a third TEID that are of the base station, and identifiesa first path between the base station and the UPF. The second accessnetwork tunnel information includes a fourth IP address and a fourthTEID that are of the base station, and identifies a second path betweenthe base station and the UPF. The third TEID and the fourth TEID aredifferent. The third IP address and the fourth IP address may be thesame or may be different.

When the third IP address and the fourth IP address are different, thethird IP address and the fourth IP address identify two paths that areindependent of each other.

When the third IP address and the fourth IP address are the same, thebase station further allocates third network identification informationcorresponding to the third TEID and fourth network identificationinformation corresponding to the fourth TEID. The third networkidentification information and the fourth network identificationinformation identify two paths that are independent of each other. Forthe third/fourth network identification information, refer to thedescriptions of the first network identification information. Detailsare not described herein again. In this way, when the third IP addressand the fourth IP address are the same, when subsequently sending thefirst access network tunnel information and the second access networktunnel information, the base station further sends the third networkidentification information corresponding to the third TEID and thefourth network identification information corresponding to the fourthTEID. Details are not described below again. For example, the basestation may send the first access network tunnel information and thethird network identification information using a third container, andsend the second access network tunnel information and the fourth networkidentification information using a fourth container.

Step 507. The base station sends the first access network tunnelinformation and the second access network tunnel information to the AMF.

For example, the base station returns an N2 session response to the AMF.The N2 session response includes the PDU session identifier and the N2SM information. The N2 SM information includes the first access networktunnel information and the second access network tunnel information.

Optionally, when the first service is at a session granularity, the N2SM information may further include a session identifier corresponding tothe first service, or when the first service is at a service flowgranularity, the N2 SM information may further include a sessionidentifier and a QFI that correspond to the first service.

Step 508. The AMF sends a context update request to the SMF.

For example, the AMF sends an Nsmf_PDUSession_UpdateSMContext request toinvoke an SM context update service Nsmf_PDUSession_UpdateSMContext ofthe SMF. The AMF forwards, to the SMF using the request, the N2 SMinformation received in step 507.

Step 509. The SMF sends a downlink forwarding rule to the UPF.

For example, the SMF sends an N4 session modification request to theUPF, and the session modification request includes the downlinkforwarding rule. The UPF returns an N4 session modification response.

It should be noted that, in another implementation, the core networktunnel information in step 503 may include only the first core networktunnel information, however, the first access network tunnel informationand the second access network tunnel information are included in step506. After receiving the first access network tunnel information and thesecond access network tunnel information, the SMF allocates second corenetwork tunnel information, sends the second core network tunnelinformation to the UPF in step 509, and sends the second core networktunnel information to the base station via the AMF, or after receivingthe first access network tunnel information and the second accessnetwork tunnel information from the SMF, the UPF allocates second corenetwork tunnel information, and returns the second core network tunnelinformation to the SMF using the N4 session modification response. TheSMF sends the second core network tunnel information to the base stationvia the AMF.

The downlink forwarding rule includes the first access network tunnelinformation and the second access network tunnel information. Thedownlink forwarding rule indicates the UPF to replicate a receiveddownlink packet of the first service, and send downlink packets of thefirst service through the two paths respectively corresponding to thefirst access network tunnel information and the second access networktunnel information, in an embodiment, send one of the downlink packetsof the first service through the first path that is between the UPF andthe base station and that corresponds to the first access network tunnelinformation, and send the other of downlink packets of the first servicethrough the second path that is between the UPF and the base station andthat corresponds to the second access network tunnel information.

Optionally, when the first service is at the session granularity, the N2SM information received by the SMF in step 508 further includes thesession identifier corresponding to the first service. Therefore, thedownlink forwarding rule further includes the session identifiercorresponding to the first service. When the first service is at theservice flow granularity, the N2 SM information received by the SMF instep 508 further includes the session identifier and the QFI thatcorrespond to the first service. Therefore, the downlink forwarding rulefurther includes the session identifier and the QFI that correspond tothe first service.

Optionally, the session identifier corresponding to the first service inthe N2 SM information received in step 508 and the session identifiercorresponding to the first service in the downlink forwarding rule maybe different, but are associated with each other. For example, thesession identifier corresponding to the first service in the N2 SMinformation received in step 508 is the PDU session identifier. The SMFconverts the PDU session identifier into an N4 session identifier, usesthe N4 session identifier as the session identifier corresponding to thefirst service in the downlink forwarding rule, and sends the N4 sessionidentifier to the UPF.

In addition, the downlink forwarding rule further includes informationabout the first service (for example, the URLLC service). Refer to thedescriptions of step 313 in FIG. 3A and FIG. 3B. Details are notdescribed herein again.

Step 510. The SMF sends a context update response to the AMF.

Then, after receiving the downlink packet of the first service, the UPFsends the downlink packets of the first service according to theforwarding rule through the first path that is between the UPF and thebase station and that corresponds to the first access network tunnelinformation, and the second path that is between the UPF and the basestation and that corresponds to the second access network tunnelinformation, separately. That the downlink packets of the first serviceare transmitted through the two paths also means that the downlinkpackets sent through the two paths are the same.

For example, after receiving a downlink packet, the UPF matches a packetheader characteristic of the downlink packet with the information aboutthe first service in the forwarding rule, to determine that the downlinkpacket is a packet of the first service. After determining that thedownlink packet is the packet of the first service, the UPF mayreplicate the packet. In a possible implementation, the UPF sends anoriginal packet to the UE through the first path that is between the UPFand the base station and that corresponds to the first access networktunnel information, and sends a replicated packet to the UE through thesecond path that is between the UPF and the base station and thatcorresponds to the second access network tunnel information. In anotherpossible implementation, the UPF sends a replicated packet to the UEthrough the first path that is between the UPF and the base station andthat corresponds to the first access network tunnel information, andsends an original packet to the UE through the second path that isbetween the UPF and the base station and that corresponds to the secondaccess network tunnel information. In still another possibleimplementation, the UPF performs packet replication to obtain twopackets, and sends the replicated packets to the UE through the firstpath and the second path that are between the UPF and the base stationand that respectively correspond to the first access network tunnelinformation and the second access network tunnel information. In theforegoing several manners, the downlink packets transmitted through thedual paths are the same.

In addition, in an uplink direction, after receiving the first corenetwork tunnel information and the second core network tunnelinformation that are included in the N2 SM information in step 504, thebase station learns that the UE may subsequently transmit an uplinkpacket of the first service through the two paths respectivelycorresponding to the first core network tunnel information and thesecond core network tunnel information. The first core network tunnelinformation and the second core network tunnel information may beconsidered as information included in an uplink forwarding rule. Theuplink forwarding rule indicates the base station to replicate areceived uplink packet of the first service, and send uplink packets ofthe first service to the UPF through the first path corresponding to thefirst access network tunnel information and the second pathcorresponding to the second access network tunnel information.

Similarly, the uplink forwarding rule further includes the informationabout the first service. Details are not described herein again. Afterdetermining, based on the information about the first service, that anuplink packet is a packet of the first service, the base station mayreplicate the packet. In a possible implementation, the base stationsends an original packet to the UPF through the first path correspondingto the first access network tunnel information, and sends a replicatedpacket to the UPF through the second path corresponding to the secondaccess network tunnel information. In another possible implementation,the base station sends a replicated packet to the UPF through the firstpath corresponding to the first access network tunnel information, andsends an original packet to the UPF through the second pathcorresponding to the second access network tunnel information. In stillanother possible implementation, the base station performs packetreplication to obtain two packets, sends one of the replicated packetsto the UPF through the first path corresponding to the first accessnetwork tunnel information, and sends the other one of the replicatedpackets to the UPF through the second path corresponding to the secondaccess network tunnel information. In the foregoing several manners, theuplink packets transmitted through the dual paths are the same.

Therefore, according to the packet transmission method in thisembodiment of the present disclosure, the uplink/downlink packets of thefirst service (for example, the URLLC service) may be transmittedthrough the two paths. Similarly, the method in this embodiment of thisapplication may further be used to transmit an uplink packet/a downlinkpacket of the first service through a plurality of (more than two)paths. Details are not described again. Therefore, reliability of packettransmission of the URLLC service is improved.

FIG. 11A and FIG. 11B are a signaling exchange diagram of a packettransmission method according to another embodiment of this application.FIG. 11A and FIG. 11B are applicable to a dual connectivity (dual basestation) scenario. In this scenario, high-reliability packettransmission is implemented through two paths between a master basestation and a UPF and between a secondary base station and the UPF. Asshown in FIG. 11A and FIG. 11B, the method includes step 1101 to step1103 in an uplink direction and/or step 1111 to step 1113 in a downlinkdirection. The following is an example.

Step 1101. For the uplink direction of dual connectivities, UE generatesa first uplink packet and a second uplink packet.

The first uplink packet and the second uplink packet have a samesequence number and a same service flow identifier. For example, the UEgenerates the first uplink packet and the second uplink packet accordingto the indication received from the master base station in step 305 or308.

For example, the UE may first replicate an uplink packet, and then add asame sequence number and a same service flow identifier, or the UE mayfirst add a sequence number and a service flow identifier to an uplinkpacket, and then replicate the uplink packet. Regardless of whichmanner, the first uplink packet and the second uplink packet that aregenerated by the UE have a same sequence number and a same service flowidentifier.

Then, the UE sends the first uplink packet to the master base station,and sends the second uplink packet to the secondary base station.

Step 1102. After receiving the first uplink packet, the master basestation determines that the first uplink packet corresponds to the dualbase stations, and processes the first uplink packet. Similarly, afterreceiving the second uplink packet, the secondary base stationdetermines that the second uplink packet corresponds to the dual basestations, and processes the second uplink packet.

For example, because the master base station determines to add thesecondary base station in step S306, after receiving the first uplinkpacket, the master base station may learn that the first uplink packetcorresponds to the dual base stations, and further perform conventionalprocessing on the first uplink packet. After receiving the second uplinkpacket, the secondary base station as a second base station in the dualconnectivities may learn that the second uplink packet corresponds tothe dual base stations, and further perform conventional processing onthe second uplink packet.

The conventional processing herein includes but is not limited todecapsulation at a physical layer, a layer 2, and the like,encapsulation at a GTP-U layer, a user datagram protocol (UDP)/an IPlayer, and the like, and QoS management.

Then, the master base station sends the processed first uplink packet tothe UPF through a first tunnel in dual tunnels. The secondary basestation sends the processed second uplink packet to the UPF through asecond tunnel in the dual tunnels.

Step 1103. After receiving the first uplink packet and the second uplinkpacket, the UPF deduplicates the first uplink packet and the seconduplink packet according to a forwarding rule and based on the serviceflow identifier and the sequence number that are in the first uplinkpacket and the second uplink packet.

For example, the UPF deduplicates, according to the forwarding rule, thefirst uplink packet and the second uplink packet that have the sameservice flow identifier and the same sequence number.

It should be noted that, when there are no repeated sequence numbers ofdifferent service flows, for example, the UE sequentially adds asequence number to a packet in a packet sequence, the UPF may furtherdeduplicate, according to the forwarding rule, the first uplink packetand the second uplink packet that have the same sequence number.

Step 1111. For the downlink direction of the dual connectivities, theUPF generates a first downlink packet and a second downlink packetaccording to the forwarding rule.

For example, the UPF adds a sequence number and a service flowidentifier to the downlink packets according to the forwarding rule. Inother words, the first downlink packet and the second downlink packetthat are generated by the UPF have the same sequence number and the sameservice flow identifier.

For example, the UPF may first replicate a downlink packet, and then adda same sequence number and a same service flow identifier to thedownlink packets, or the UPF may first add a sequence number and aservice flow identifier to a downlink packet, and then replicate thedownlink packet.

Then, the UPF sends the first downlink packet to the master basestation, and sends the second downlink packet to the secondary basestation.

Step 1112. After receiving the first downlink packet, the master basestation determines that the first downlink packet corresponds to thedual base stations, and processes the first downlink packet. Similarly,after receiving the second downlink packet, the secondary base stationdetermines that the second downlink packet corresponds to the dual basestations, and processes the second downlink packet.

How the master base station determines that the first downlink packetcorresponds to the dual base stations and how the secondary base stationdetermines that the second downlink packet corresponds to the dual basestations are not described in detail again.

The processing in step 1112 includes but is not limited to decapsulationat the UDP/IP layer, the GTP-U layer, and the like, encapsulation at thelayer 2, the physical layer, and the like, and QoS management.

Then, the master base station sends the processed first downlink packetto the UE. The secondary base station sends the processed seconddownlink packet to the UE. The first downlink packet and the seconddownlink packet include a same second service flow identifier and a samesecond sequence number.

Step 1113. After receiving the first downlink packet and the seconddownlink packet from the master base station and the secondary basestation respectively, the UE deduplicates the first downlink packet andthe second downlink packet according to the indication from the masterbase station and based on the service flow identifier and the sequencenumber that are in the first downlink packet and the second downlinkpacket. For example, the UE deduplicates, according to the indicationreceived from the master base station in step 305 or 308, the firstdownlink packet and the second downlink packet that have the sameservice flow identifier and the same sequence number.

It should be noted that, when there are no repeated sequence numbers ofdifferent service flows, for example, the UPF sequentially adds asequence number to a packet in a packet sequence, the UE may furtherdeduplicate, according to the indication received from the master basestation, the first downlink packet and the second downlink packet thathave the same sequence number.

Then, the UE performs decapsulation at the physical layer, the layer 2,and the like, and transmits a decapsulated packet to an upper layer.

FIG. 12A and FIG. 12B are a signaling exchange diagram of a packettransmission method according to another embodiment of this application.FIG. 12A and FIG. 12B are applicable to a single connectivity (singlebase station) scenario. In this scenario, high-reliability packettransmission is implemented through two paths between the single basestation and a UPF. As shown in FIG. 12A and FIG. 12B, the methodincludes step 1201 to step 1203 in an uplink direction and/or step 1211to step 1213 in a downlink direction. The following is an example.

Step 1201. For the uplink direction of a single connectivity, UE adds aservice flow identifier to an uplink packet.

Then, the UE sends the uplink packet to the base station.

Step 1202. After receiving the uplink packet, the base stationdetermines that the uplink packet corresponds to the single basestation, generates a first uplink packet and a second uplink packet, andprocesses the first uplink packet and the second uplink packet.

For example, if the base station determines, in the foregoing stepprocedure, not to add a secondary base station, the base station maylearn, after receiving the uplink packet, that the uplink packetcorresponds to the single base station, further generate the firstuplink packet and the second uplink packet, and process the first uplinkpacket and the second uplink packet.

For example, the base station may first replicate an uplink packet, andthen add a same sequence number and a same service flow identifier tothe uplink packets, or the base station may first add a sequence numberand a service flow identifier to an uplink packet, and then replicatethe uplink packet. Regardless of which manner, the first uplink packetand the second uplink packet that are generated by the base station havea same sequence number and a same service flow identifier.

The processing herein includes but is not limited to decapsulation at aphysical layer, a layer 2, and the like, encapsulation at a GTP-U layer,a UDP/an IP layer, and the like, and QoS management.

Then, the base station sends the processed first uplink packet to theUPF through a first tunnel in dual tunnels, and sends the processedsecond uplink packet to the UPF through a second tunnel in the dualtunnels.

Step 1203. After receiving the first uplink packet and the second uplinkpacket, the UPF deduplicates the first uplink packet and the seconduplink packet according to a forwarding rule and based on the serviceflow identifier and the sequence number that are in the first uplinkpacket and the second uplink packet.

For example, the UPF deduplicates, according to the forwarding rule, thefirst uplink packet and the second uplink packet that have the sameservice flow identifier and the same sequence number.

It should be noted that, when there are no repeated sequence numbers ofdifferent service flows, for example, the base station sequentially addsa sequence number to a packet in a packet sequence, the UPF may furtherdeduplicate, according to the forwarding rule, the first uplink packetand the second uplink packet that have the same sequence number.

Step 1211. For the downlink direction of the single connectivity, theUPF generates a first downlink packet and a second downlink packetaccording to the forwarding rule.

For step 1211, refer to the descriptions of step 1111. Details are notdescribed herein again.

Then, the UPF sends the first downlink packet and the second downlinkpacket to the base station through the first tunnel and the secondtunnel respectively.

Step 1212. After receiving the first downlink packet and the seconddownlink packet, the base station determines that the first downlinkpacket and the second downlink packet correspond to the single basestation, deduplicates the first downlink packet and the second downlinkpacket according to an indication of the base station and based on theservice flow identifier and the sequence number that are in the firstdownlink packet and the second downlink packet, and processes thededuplicated downlink packet.

How the base station determines that the first downlink packet and thesecond downlink packet correspond to the single base station is notdescribed in detail again.

For example, the base station deduplicates the first downlink packet andthe second downlink packet based on the service flow identifier and thesequence number that are in the first downlink packet and the seconddownlink packet. For example, the base station deduplicates the firstdownlink packet and the second downlink packet that have the sameservice flow identifier and the same sequence number.

It should be noted that, when there are no repeated sequence numbers ofdifferent service flows, for example, the UPF sequentially adds asequence number to a packet in a packet sequence, the base stationdeduplicates the first downlink packet and the second downlink packetthat have the same sequence number.

Subsequent processing includes but is not limited to decapsulation atthe UDP/IP layer, the GTP-U layer, and the like, encapsulation at thelayer 2, the physical layer, and the like, and QoS management.

Then, the base station sends the processed downlink packet to the UE.

Step 1213. After receiving the downlink packet from the base station,the UE performs decapsulation at the physical layer, the layer 2, andthe like, and transmits a decapsulated packet to an upper layer.

FIG. 15A and FIG. 15B are a signaling exchange diagram of another packettransmission method according to an embodiment of this application. FIG.15A and FIG. 15B relate to interaction between UE, a master basestation, a secondary base station, an AMF, an SMF, and a UPF. Forexample, the UE, the master base station, the secondary base station,the AMF, the SMF, and the UPF may be respectively the UE 201, the M-RAN202, the S-RAN 203, the AMF 204, the SMF 205, and the UPF 206 in FIG. 2.FIG. 15A and FIG. 15B are described with reference to FIG. 3A and FIG.3B.

For example, FIG. 15A and FIG. 15B are applicable to a case in which inan uplink direction, a PDCP layer of the UE is enhanced, and a packetcan be replicated at the enhanced PDCP layer, in a downlink direction,the UPF can replicate a packet at a GTP-U layer such that dual-pathpacket transmission is implemented and packet transmission reliabilityis improved.

As shown in FIG. 15A and FIG. 15B, the method includes the followingsteps.

Step 1501. The UE sends, to the AMF via the master base station, a NASmessage that carries a session establishment request, to request toestablish a PDU session for the UE.

Step 1502. Other steps of a session establishment procedure areperformed.

For example, the foregoing other steps include at least the AMF selectsthe SMF, and the SMF selects the UPF. Details are not described herein.

Step 1503. The SMF transmits N2 SM information to the AMF.

Step 1504. The AMF sends the N2 SM information to the master basestation.

For step 1501 to step 1504, refer to the descriptions of step 301 tostep 304 in FIG. 3A and FIG. 3B. Details are not described herein again.

Step 1505. The master base station initiates establishment of an accessnetwork resource between the master base station and the UE.

In other words, the master base station initiates establishment of afirst radio bearer between the master base station and the UE. Forexample, the first radio bearer is a first data radio bearer (DRB),which is referred to as a DRB 1 for short below. In this step, themaster base station sends identification information of the DRB 1 to theUE. The DRB 1 between the master base station and the UE is establishedthrough this step.

Step 1506. The master base station determines to add the secondary basestation, and sends a secondary base station adding request to thesecondary base station.

The master base station may determine, based on indication information,to transmit an uplink packet of a first service through dual paths, todetermine that the secondary base station needs to be added. The firstservice includes a URLLC service. For example, any one or a combinationof a QoS parameter, slice identification information, a DNN, and firstcore network tunnel information and second core network tunnelinformation that are included in the N2 SM information may be used asthe indication information. The QoS parameter includes at least one of a5QI and a QFI. For example, if the master base station determines, basedon the QoS parameter in the N2 SM information, that the session requireshigh reliability, the master base station determines to add thesecondary base station, or if the master base station determines, basedon the slice identification information in the N2 SM information, thatthe session is associated with a slice in URLLC, the master base stationdetermines to add the secondary base station, or if the master basestation determines, based on the DNN in the N2 SM information, that thesession is associated with a DN in URLLC, the master base stationdetermines to add the secondary base station, or if the master basestation directly determines, based on the first core network tunnelinformation and the second core network tunnel information in the N2 SMinformation, to transmit the uplink packet through the dual paths, themaster base station determines to add the secondary base station.Because the first access network tunnel information and the secondaccess network tunnel information need to be used for transmission ofthe downlink packet through the dual paths, it may further be consideredthat the indication information triggers determining of the first accessnetwork tunnel information and the second access network tunnelinformation. The first access network tunnel information may bedetermined by the master base station, and the second access networktunnel information may be determined by the secondary base station andsent to the master base station.

For details about the first access network tunnel information and thesecond access network tunnel information, refer to the descriptions ofFIG. 3A and FIG. 3B. Details are not described herein again.

Step 1507. The secondary base station returns a secondary base stationadding request acknowledgment to the master base station.

For example, the secondary base station adding request acknowledgmentincludes the second access network tunnel information determined by thesecondary base station.

Optionally, if the first service is at a session granularity, thesecondary base station adding request sent in step 1506 includes asession identifier of the first service. Therefore, the second accessnetwork tunnel information determined by the secondary base station isalso at the session granularity and corresponds to the sessionidentifier. If the first service is at a service flow granularity, thesecondary base station adding request sent in step 1506 includes aservice flow identifier (for example, a QFI) of a service flow of thefirst service. Therefore, the second access network tunnel informationdetermined by the secondary base station is also at the service flowgranularity and corresponds to the service flow identifier. From aperspective of a protocol stack, the master base station generates aPDCP entity for the service flow. Therefore, the service flow isassociated with the PDCP entity. If the master base station determinesto add the secondary base station, the secondary base station alsogenerates a PDCP entity for the service flow.

Step 1508. The master base station initiates RRC connectionreconfiguration to the UE.

In other words, the master base station initiates establishment of asecond radio bearer between the secondary base station and the UE. Forexample, the second radio bearer is a DRB 2. In this step, the masterbase station sends identification information of the DRB 2 to the UE.The DRB 2 between the secondary base station and the UE is establishedthrough this step.

In step 1508, the master base station sends indication information tothe UE, and the indication information indicates the UE to associate thefirst radio bearer and the second radio bearer with a same PDCP entityon the UE. That is, the first radio bearer and the second radio bearerare associated with each other. In other words, the master base stationsends the indication information to the UE using an RRC message.Specifically, the indication information may be a new informationelement, or may be an identifier of the DRB 1, or may be anotherinformation element. This is not limited in this application.

The indication information indicates the UE to associate the first radiobearer and the second radio bearer with the same PDCP entity on the UE.It may also be understood that after receiving the indicationinformation, the UE replicates an uplink packet at a PDCP layer (in anembodiment, adds a same sequence number at the PDCP layer), to obtain afirst uplink packet and a second uplink packet, and then send the firstuplink packet and the second uplink packet over two different radiobearers (for example, the DRB 1 and the DRB 2) associated with the PDCPentity respectively.

Step 1509. The master base station feeds back secondary base stationreconfiguration completion to the secondary base station, to notify thesecondary base station that the UE successfully completes the RRCconnection reconfiguration.

Optionally, if the secondary base station has an RRC function, theforegoing step 1507 to step 1509 may be replaced with the followingsteps.

1507′. The secondary base station initiates an RRC connectionestablishment process to the UE.

In other words, the secondary base station initiates establishment of asecond radio bearer between the secondary base station and the UE. Forexample, the second radio bearer is a DRB 2. The DRB 2 between thesecondary base station and the UE is established through this step.

In step 1507′, the secondary base station sends indication informationto the UE, and the indication information indicates the UE to associatethe first radio bearer and the second radio bearer with a same PDCPentity on the UE. That is, the first radio bearer and the second radiobearer are associated with each other. In other words, the secondarybase station sends the indication information to the UE using an RRCmessage. Specifically, the indication information may be a newly addedinformation element, or may be an identifier of the DRB 1, or may beanother information element. This is not limited in this application.Therefore, the indication information indicating the UE to associate thefirst radio bearer and the second radio bearer with the same PDCP entityon the UE may be sent by the master base station to the UE, or may besent by the secondary base station to the UE. This is not limited inthis application.

1508′. The secondary base station returns a secondary base stationadding request acknowledgment to the master base station. For details,refer to the descriptions of step 1507. Details are not described again.

Step 1510. Random access procedure is performed.

Optionally, in another embodiment, the master base station maydetermine, before step 1505, whether the secondary base station needs tobe added. For how the master base station determines whether a secondarybase station needs to be added, refer to the descriptions of step 1506.Details are not described herein again. If the master base stationdetermines to add the secondary base station (in an embodiment, transmita packet in a dual connectivity manner), the master base station maysend, to the UE through step 1508 or step 1507′, the indicationinformation for associating the two DRBs with one PDCP entity.

It may be understood that the UE may process the uplink packet invarious manners, and a plurality of processed uplink packets have a samesequence number. For example, the UE may first add a sequence number toa first uplink packet, and then replicate the first uplink packet towhich the sequence number is added, to obtain a second uplink packethaving the same sequence number, or the UE may first replicate a firstuplink packet to obtain a second uplink packet, and then add a samesequence number to the first uplink packet and the second uplink packet.This is not limited in this application.

Optionally, the master base station further indicates the UE todeduplicate received downlink packets that have a same sequence numberand correspond to a same service flow identifier.

Optionally, in still another embodiment, the N2 SM informationtransmitted in the foregoing step 1503 and step 1504 further includesindication information, and the indication information indicates thebase station (namely, the master base station) to send, to the UE, theindication information for associating the first radio bearer and thesecond radio bearer with the same PDCP entity on the UE. For example,when the SMF determines, based on the QFI in the N2 SM information sentby the UE to the SMF, that the session requires high reliability, and/ordetermines, based on the slice identification information in the N2 SMinformation, that the session is associated with a slice in URLLC,and/or determines, based on the DNN in the N2 SM information, that thesession is associated with a DN in URLLC, and/or determines, based onsubscription data of the UE, that the UE is UE in URLLC, the SMF sendsthe indication information to the base station, and after the basestation receives the indication information, the base station sends, tothe UE, the indication information for associating the first radiobearer and the second radio bearer with the same PDCP entity on the UE.In this way, the base station may not perform determining, therebysimplifying an operation on a base station side.

Step 1511. The master base station sends the first access network tunnelinformation and the second access network tunnel information to the AMF.

Step 1512. The AMF sends a context update request to the SMF.

Step 1513. The SMF sends a downlink forwarding rule to the UPF.

Step 1514. The SMF sends a context update response to the AMF.

For step 1511 to step 1514, refer to the descriptions of step 311 tostep 314 in FIG. 3A and FIG. 3B. Details are not described herein again.

Then, the UE may generate a first packet and a second packet based onthe indication information, where the first packet and the second packethave a same sequence number. The UE sends the first packet to the masterbase station over the first radio bearer, and sends the second packet tothe secondary base station over the second radio bearer. For example,the UE replicates a packet at the PDCP layer based on the indicationinformation, to obtain the first packet and the second packet. Inaddition, the UE may deduplicate, based on the indication information,the downlink packets that are from the first radio bearer and the secondradio bearer and that have the same sequence number.

Therefore, according to the packet transmission method in thisembodiment of the present disclosure, the uplink packet of the firstservice (for example, the URLLC service) may be transmitted through thetwo paths. Similarly, the method in this embodiment of this applicationmay further be used to transmit the uplink packet of the first servicethrough a plurality of (more than two) paths. Details are not describedagain. Therefore, reliability of packet transmission of the URLLCservice is improved.

With reference to the descriptions of FIG. 15A and FIG. 15B, anembodiment of this application provides a packet transmission method. Asshown in FIG. 16, the method includes the following steps.

Step 1601. A first base station initiates establishment of a first radiobearer between the first base station and UE.

For example, the first base station may be the master base station inFIG. 15A and FIG. 15B, and the first radio bearer may be the DRB 1. Forstep 1601, refer to the descriptions of step 1505 in FIG. 15A and FIG.15B. Details are not described again.

Step 1602. In a process of establishing a second radio bearer between asecond base station and the UE, the first base station or the secondbase station sends indication information to the UE, where theindication information indicates the UE to associate the first radiobearer and the second radio bearer with a same PDCP entity on the UE.

For example, the first base station or the second base station sends theindication information to the UE using an RRC layer message.

For example, the second base station may be the secondary base stationin FIG. 15A and FIG. 15B, and the second radio bearer may be the DRB 2.For step 1602, refer to the descriptions of step 1508 or 1507′ in FIG.15A and FIG. 15B. Details are not described again.

According to the foregoing method, after receiving the indicationinformation, the UE replicates a packet at a PDCP layer (in anembodiment, adds a same sequence number at the PDCP layer), to obtain afirst uplink packet and a second uplink packet, and then sends the firstuplink packet and the second uplink packet over two different radiobearers (for example, the DRB 1 and the DRB 2) associated with the PDCPentity respectively. Therefore, according to the packet transmissionmethod in this embodiment of the present disclosure, an uplink packet ofa first service (for example, a URLLC service) may be transmittedthrough two paths. Similarly, the method in this embodiment of thisapplication may further be used to transmit the uplink packet of thefirst service through a plurality of (more than two) paths. Details arenot described again. Therefore, reliability of packet transmission ofthe URLLC service is improved.

With reference to the descriptions of FIG. 15A and FIG. 15B, anembodiment of this application provides a packet transmission method. Asshown in FIG. 17, the method includes the following steps.

Step 1701. UE interacts with a first base station, to establish a firstradio bearer between the first base station and the UE.

For example, the first base station may be the master base station inFIG. 15A and FIG. 15B, and the first radio bearer may be the DRB 1. Forstep 1701, refer to the descriptions of step 1505 in FIG. 15A and FIG.15B. Details are not described again.

Step 1702. In a process of establishing a second radio bearer between asecond base station and the UE, the UE receives indication informationfrom the first base station or the second base station, where theindication information indicates the UE to associate the first radiobearer and the second radio bearer with a same PDCP entity on the UE.

For example, the second base station may be the secondary base stationin FIG. 15A and FIG. 15B, and the second radio bearer may be the DRB 2.For step 1702, refer to the descriptions of step 1508 or 11507′ in FIG.15A and FIG. 15B. Details are not described again.

That is, the UE receives the indication information from the first basestation or the second base station using an RRC layer message.

Step 1703. The UE generates a first packet and a second packet based onthe indication information, where the first packet and the second packethave a same sequence number.

For example, the UE replicates a packet at a PDCP layer based on theindication information, to obtain the first packet and the secondpacket.

Step 1704. The UE sends the first packet to the first base station overthe first radio bearer, and sends the second packet to the second basestation over the second radio bearer.

According to the foregoing method, after receiving the indicationinformation, the UE replicates an uplink packet at the PDCP layer (in anembodiment, adds a same sequence number at the PDCP layer), to obtain afirst uplink packet and a second uplink packet, sends the first uplinkpacket and the second uplink packet over two different radio bearers(for example, the DRB 1 and the DRB 2) associated with the PDCP entityrespectively, and deduplicates, at the PDCP layer, downlink packets thatare from the DRB 1 and the DRB 2 and that have a same sequence number.Therefore, according to the packet transmission method in thisembodiment of the present disclosure, an uplink packet of a firstservice (for example, a URLLC service) may be transmitted through twopaths. Similarly, the method in this embodiment of this application mayfurther be used to transmit the uplink packet of the first servicethrough a plurality of (more than two) paths. Details are not describedagain. Therefore, reliability of packet transmission of the URLLCservice is improved.

FIG. 18A and FIG. 18B are a signaling exchange diagram of another packettransmission method according to an embodiment of this application. FIG.18A and FIG. 18B relate to interaction between UE, a master basestation, a secondary base station, an AMF, an SMF, and a UPF. Forexample, the UE, the master base station, the secondary base station,the AMF, the SMF, and the UPF may be respectively the UE 201, the M-RAN202, the S-RAN 203, the AMF 204, the SMF 205, and the UPF 206 in FIG. 2.FIG. 18A and FIG. 18B are described with reference to FIG. 3A and FIG.3B.

For example, FIG. 18A and FIG. 18B are applicable to a case in which inan uplink direction, the UE replicates a packet at a new protocol layerabove an SDAP layer, in a downlink direction, the UPF replicates apacket at a new protocol layer on a GTP-U layer such that dual-pathpacket transmission is implemented and packet transmission reliabilityis improved. For example, the new protocol layer may be referred to as aHRP layer.

As shown in FIG. 18A and FIG. 18B, the method includes the followingsteps.

Step 1801. The UE sends, to the AMF via the master base station, a NASmessage that carries a session establishment request, to request toestablish a PDU session for the UE.

Step 1802. Other steps of a session establishment procedure areperformed.

For example, the foregoing other steps include at least the AMF selectsthe SMF, and the SMF selects the UPF. Details are not described herein.

For step 1801 and step 1802, refer to the descriptions of step 301 andstep 302 in FIG. 3A and FIG. 3B. Details are not described herein again.

Step 1803. The SMF allocates, to a first service, two service flowidentifiers, namely, a first service flow identifier and a secondservice flow identifier. The first service includes a URLLC service. Theservice flow identifier may include at least one of a sessionidentifier, a QFI, and a 5-tuple. For example, the two service flowidentifiers are respectively a QFI-a and a QFI-b.

Step 1804. The SMF transmits N2 SM information and an N1 SM container tothe AMF.

For example, the SMF sends the N2 SM information to the AMF by invokingan N1N2 message transfer service of the AMF. In addition, the SMF mayfurther send, to the AMF by invoking the service, the N1 SM containerincluding a session accept message.

Step 1805. The AMF sends the received N2 SM information and the receivedN1 SM container to the master base station.

For example, the AMF sends an N2 session request to the master basestation, and the N2 session request includes the N2 SM information and aNAS message. The NAS message includes the PDU session identifier and theN1 SM container. The master base station sends the NAS message to the UEin a process of establishing an access network resource.

The N1 SM container includes the session accept message to be sent tothe UE. The session accept message includes a QoS rule. For example, theQoS rule includes a QoS rule identifier, the first service flowidentifier, the second service flow identifier, a packet filter, andindication information.

The N2 SM information includes at least the PDU session identifier andcore network tunnel information. The core network tunnel informationincludes first core network tunnel information and second core networktunnel information. For details, refer to the descriptions of FIG. 3Aand FIG. 3B. Details are not described herein again. The N2 SMinformation may further include a QoS parameter, the QFI-a, the QFI-b,slice identification information (for example, S-NSSAI), a session-AMBR,and a PDU session type. Optionally, the N2 SM information may furtherinclude a DNN.

The UE may receive the indication information using the N1 SM container.In the uplink direction, the UE may generate a first uplink packet and asecond uplink packet based on the indication information, send the firstuplink packet over a first radio bearer, and send the second uplinkpacket over a second radio bearer. In addition, the first uplink packetand the second uplink packet have a same first sequence number. Thefirst radio bearer corresponds to the QFI-a, and the second radio bearercorresponds to the QFI-b. That the UE sends the first uplink packet overthe first radio bearer may also be described as that the UE sends thefirst uplink packet over a radio bearer corresponding to the QFI-a. Thatthe UE sends the second uplink packet over the second radio bearer mayalso be described as that the UE sends the second uplink packet over aradio bearer corresponding to the QFI-b. For example, the indicationinformation indicates the UE to replicate an uplink packet to obtain thefirst uplink packet and the second uplink packet, and send the firstuplink packet and the second uplink packet over different radio bearers.In addition, in the downlink direction, the UE may deduplicate, based onthe indication information, downlink packets that are from the firstradio bearer and the second radio bearer and that have a same sequencenumber. It may alternatively be described as follows. The UE performsthe following operation on downlink packet from the radio bearercorresponding to the QFI-a and the downlink packet from the radio bearercorresponding to the QFI-b, if the downlink packets have a same sequencenumber, deduplicating the downlink packets.

For example, the UE determines, using the packet filter, packetscorresponding to the QFI-a and the QFI-b, and replicates the packets atthe HRP layer based on the indication information. The replicated uplinkpackets have a same sequence number and respectively correspond to theQFI-a and the QFI-b such that the first uplink packet corresponding tothe QFI-a and the second uplink packet corresponding to the QFI-b areobtained. Then, the first uplink packet and the second uplink packet aretransmitted to the SDAP layer. The UE sends, at the SDAP layer based ona correspondence between a QFI and a PDCP entity, the first uplinkpacket to a PDCP entity 1, and sends the second uplink packet to a PDCPentity 2, where the PDCP entity 1 corresponds to the QFI-a, and the PDCPentity 2 corresponds to the QFI-b. Similarly, after the first uplinkpacket and the second uplink packet are processed at another protocollayer such as a radio link control (RLC) layer or a physical layer, theUE sends the first uplink packet to the M-RAN over the DRB 1, and sendsthe second uplink packet to the S-RAN over the DRB 2. The DRB 1corresponds to the PDCP entity 1, and the DRB 2 corresponds to the PDCPentity 2. After receiving the two uplink packets over the DRB 1 and theDRB 2 respectively, the master base station and the secondary basestation add QFIs to the uplink packets based on a correspondence betweena DRB and a QFI or based on QFIs carried in headers of the uplinkpackets. Specifically, the master base station adds the QFI-a to thefirst uplink packet, the secondary base station adds the QFI-b to thesecond uplink packet, and the master base station and the secondary basestation send the uplink packets to the UPF. Therefore, the UPF receivesthe first uplink packet and the second uplink packet, and the firstuplink packet and the second uplink packet respectively have the QFI-aand the QFI-b and have the same sequence number.

It should be noted that, another implementation of determining, by theUE using the packet filter, packets corresponding to the QFI-a and theQFI-b is that the UE determines, using the packet filter, a QFI (whichmay be the QFI-a or the QFI-b) corresponding to a packet. Because theQFI-a and the QFI-b are two service flow identifiers allocated by theSMF to a same service, it may be understood that the QFI-a and the QFI-bare associated such that the UE replicates an uplink packet based on theindication information, where one uplink packet corresponds to theQFI-a, and the other uplink packet corresponds to the QFI-b.

In other words, the first uplink packet sent by the UE corresponds tothe QFI-a, the second uplink packet sent by the UE corresponds to theQFI-b, and the first uplink packet and the second uplink packet have thesame sequence number. The first uplink packet received by the UPFincludes the QFI-a, the second uplink packet received by the UPFincludes the QFI-b, and the first uplink packet and the second uplinkpacket have the same sequence number. The sequence numbers and theservice flow identifiers of the first uplink packet and the seconduplink packet that are received by the UPF may be at different protocollayers. For example, the sequence number is at the HRP layer, and theservice flow identifier is at the GTP-U layer.

In a possible implementation, the indication information sent by the SMFto the UE may indicate that the first uplink packet corresponds to theQFI-a, and the second uplink packet corresponds to the QFI-b. In anotherpossible implementation, the UE may further add the QFI-a to the firstuplink packet and add the QFI-b to the second uplink packet at the HRPlayer. Further, the indication information sent by the SMF to the UE mayindicate the UE to add the QFI-a to the first uplink packet and add theQFI-b to the second uplink packet.

It may also be understood that the UE associates the first uplink packetand the second uplink packet that are obtained after the replicationwith different DRBs, PDCP entities, or SDAP configurations. One PDCPentity or SDAP configuration corresponds to one DRB (for example, theDRB 1), and the other PDCP entity or SDAP configuration corresponds tothe other DRB (for example, the DRB 2). The SDAP configuration is aparameter at a radio bearer granularity (namely, a DRB granularity), andis allocated by an access network side based on the bearer granularityand sent to the UE in an RRC reconfiguration process.

In addition, in the downlink direction, when the UE receives a firstdownlink packet and a second downlink packet from the master basestation and the secondary base station respectively, where the firstdownlink packet and the second downlink packet have a same sequencenumber and respectively correspond to the QFI-a and the QFI-b, the UEdeduplicates the first downlink packet and the second downlink packetbased on the indication information. Therefore, further, optionally, theindication information sent by the SMF to the UE may further indicatethe UE to deduplicate the first downlink packet and the second downlinkpacket. The first downlink packet and the second downlink packet havethe same sequence number, and are respectively associated with the QFI-aand the QFI-b.

Step 1806. The master base station initiates establishment of the accessnetwork resource between the master base station and the UE.

In other words, the master base station initiates establishment of thefirst radio bearer between the master base station and the UE. Forexample, the first radio bearer is the DRB 1. In this step, the masterbase station sends identification information of the DRB 1 to the UE.The DRB 1 between the master base station and the UE is establishedthrough this step. In addition, in this step, the master base stationforwards the NAS message in step 1805 to the UE.

Step 1807. The master base station determines to add the secondary basestation, and sends a secondary base station adding request to thesecondary base station.

The master base station may determine, based on the indicationinformation, to transmit the uplink packet of the first service throughdual paths, to determine that the secondary base station needs to beadded. The first service includes the URLLC service. For example, anyone or a combination of the QoS parameter, the slice identificationinformation, the DNN, and the first core network tunnel information andthe second core network tunnel information that are included in the N2SM information may be used as the indication information. The QoSparameter includes at least one of a 5QI and a QFI. Because the firstaccess network tunnel information and the second access network tunnelinformation need to be used for transmission of the downlink packetthrough the dual paths, it may further be considered that the indicationinformation triggers determining of the first access network tunnelinformation and the second access network tunnel information. The firstaccess network tunnel information may be determined by the master basestation, and the second access network tunnel information may bedetermined by the secondary base station and sent to the master basestation.

For details about the first access network tunnel information and thesecond access network tunnel information, refer to the descriptions ofFIG. 3A and FIG. 3B. Details are not described herein again.

In this step, the secondary base station adding request carries theQFI-b and the second core network tunnel information.

Step 1808. The secondary base station returns a secondary base stationadding request acknowledgment to the master base station.

For example, the secondary base station adding request acknowledgmentincludes the second access network tunnel information determined by thesecondary base station.

In other words, the secondary base station adding request sent in step1807 includes the service flow identifier QFI-b of the first service.Therefore, the second access network tunnel information determined bythe secondary base station is also at a service flow granularity andcorresponds to the QFI-b. From a perspective of a protocol stack, if themaster base station determines to add the secondary base station, themaster base station generates a PDCP entity for the QFI-a, and afterreceiving the secondary base station adding request, the secondary basestation generates a PDCP entity for the QFI-b. Therefore, the two PDCPentities are respectively associated with the QFI-a and the QFI-b.

Step 1809. The master base station initiates RRC connectionreconfiguration to the UE.

In other words, the master base station initiates establishment of thesecond radio bearer between the secondary base station and the UE. Forexample, the second radio bearer is the DRB 2. In this step, the masterbase station sends identification information of the DRB 2 to the UE.The DRB 2 between the secondary base station and the UE is establishedthrough this step.

Step 1810. The master base station feeds back secondary base stationreconfiguration completion to the secondary base station, to notify thesecondary base station that the UE successfully completes the RRCconnection reconfiguration.

Optionally, if the secondary base station has an RRC function, theforegoing step 1808 to step 1810 may be replaced with the followingsteps.

1808′. The secondary base station initiates an RRC connectionestablishment process to the UE.

In other words, the secondary base station initiates establishment ofthe second radio bearer between the secondary base station and the UE.For example, the second radio bearer is the DRB 2. In this step, thesecondary base station sends identification information of the DRB 2 tothe UE. The DRB 2 between the secondary base station and the UE isestablished through this step.

1809′. The secondary base station returns a secondary base stationadding request acknowledgment to the master base station. For details,refer to the descriptions of step 1808. Details are not described again.

Step 1811. Random access procedure is performed.

Step 1812. The master base station sends the first access network tunnelinformation and the second access network tunnel information to the AMF.The first access network tunnel information corresponds to the QFI-a,and the second access network tunnel information corresponds to theQFI-b. Optionally, the master base station further sends, to the AMF, acorrespondence between the QFI-a and the first access network tunnelinformation and a correspondence between the QFI-b and the second accessnetwork tunnel information.

For example, the master base station returns an N2 session response tothe AMF. The N2 session response includes the PDU session identifier andthe N2 SM information. The N2 SM information includes the first accessnetwork tunnel information and the second access network tunnelinformation. Optionally, the N2 SM information may further include thecorrespondence between the QFI-a and the first access network tunnelinformation and the correspondence between the QFI-b and the secondaccess network tunnel information.

Step 1813. The AMF sends a context update request to the SMF, to forwardthe received N2 SM information to the SMF.

For example, the AMF sends an Nsmf_PDUSession_UpdateSMContext request byinvoking an SM context update service of the SMF. The AMF forwards, tothe SMF using the request, the N2 SM information received in step 1812.

Step 1814. The SMF sends a forwarding rule to the UPF.

For example, the SMF sends an N4 session modification request to theUPF, and the session modification request includes the forwarding rule.The UPF returns an N4 session modification response. The forwarding rulemay include an uplink forwarding rule and a downlink forwarding rule.

The uplink forwarding rule indicates the UPF to deduplicate the tworeceived uplink packets that respectively have the QFI-a and the QFI-band have the same sequence number. Therefore, in the uplink direction,when the UPF receives the first uplink packet and the second uplinkpacket, the first uplink packet has the first service flow identifierand the first sequence number, and the second uplink packet has thesecond service flow identifier and the first sequence number. The UPFdeduplicates the first uplink packet and the second uplink packetaccording to the uplink forwarding rule.

The downlink forwarding rule includes the first access network tunnelinformation and the second access network tunnel information. Thedownlink forwarding rule further includes the QFI-a corresponding to thefirst access network tunnel information and the QFI-b corresponding tothe second access network tunnel information. The downlink forwardingrule indicates the UPF to replicate a received downlink packet of thefirst service (add the QFI-a and the sequence number to the firstdownlink packet, and add the QFI-b and the same sequence number to thesecond downlink packet), and send the downlink packets of the firstservice through the two paths respectively corresponding to the firstaccess network tunnel information and the second access network tunnelinformation, in an embodiment, send the first downlink packet to themaster base station through a first path corresponding to the firstaccess network tunnel information, and send the second downlink packetto the secondary base station through a second path corresponding to thesecond access network tunnel information. Therefore, in the downlinkdirection, the UPF generates the first downlink packet and the seconddownlink packet (for example, replicates a packet at the HRP layer, addsthe QFI-a and a sequence number to the first downlink packet, and addsthe QFI-b and the same sequence number to the second downlink packet)according to the downlink forwarding rule, sends the first downlinkpacket to a first base station, and sends the second downlink packet toa second base station, where the first downlink packet has the firstservice flow identifier and a second sequence number, and the seconddownlink packet has the second service flow identifier and the secondsequence number.

Step 1815. The SMF sends a context update response to the AMF.

Therefore, according to the packet transmission method in thisembodiment of the present disclosure, the uplink/downlink packets of thefirst service (for example, the URLLC service) may be transmittedthrough the two paths. Similarly, the method in this embodiment of thisapplication may further be used to transmit an uplink packet/a downlinkpacket of the first service through a plurality of (more than two)paths. Details are not described again. Therefore, reliability of packettransmission of the URLLC service is improved.

In addition, when a UE side does not include the new protocol layer HRPlayer, the foregoing operation at the HRP layer may alternatively beperformed at a PDU layer above the SDAP layer. This is not limited inthis application.

FIG. 19A and FIG. 19B are a signaling exchange diagram of another packettransmission method according to an embodiment of this application. FIG.19A and FIG. 19B relate to interaction between UE, a master basestation, a secondary base station, an AMF, an SMF, and a UPF. Forexample, the UE, the master base station, the secondary base station,the AMF, the SMF, and the UPF may be respectively the UE 201, the M-RAN202, the S-RAN 203, the AMF 204, the SMF 205, and the UPF 206 in FIG. 2.FIG. 19A and FIG. 19B are described with reference to FIG. 18A and FIG.18B.

For example, FIG. 19A and FIG. 19B are applicable to a case in which inan uplink direction, an SDAP layer of the UE is enhanced, and a packetcan be replicated at the enhanced SDAP layer, in a downlink direction,the UPF can replicate a packet at a GTP-U layer such that dual-pathpacket transmission is implemented and packet transmission reliabilityis improved.

A difference between FIG. 19A, FIG. 19B, FIG. 18A and FIG. 18B lies inthat in FIG. 18A and FIG. 18B, because an access network is unaware ofthe HRP layer, the SMF indicates, using the NAS message, the UE toprocess the packet of the URLLC service, while in FIG. 19A and FIG. 19B,because the SDAP layer is enhanced, the master base station mayindicate, using an AS layer message, the UE to process the packet of theURLLC service.

As shown in FIG. 19A and FIG. 19B, the method includes the followingsteps.

Step 1901. The UE sends, to the AMF via the master base station, a NASmessage that carries a session establishment request, to request toestablish a PDU session for the UE.

Step 1902. Other steps of a session establishment procedure areperformed.

For example, the foregoing other steps include at least the AMF selectsthe SMF, and the SMF selects the UPF. Details are not described herein.

Step 1903. The SMF allocates, to a first service, two service flowidentifiers, namely, a first service flow identifier and a secondservice flow identifier.

For step 1901 to step 1903, refer to the descriptions of step 1801 tostep 1803 in FIG. 18A and FIG. 18B. Details are not described hereinagain.

Step 1904. The SMF transmits N2 SM information and an N1 SM container tothe AMF.

For example, the SMF sends the N2 SM information to the AMF by invokingan N1N2 message transfer service of the AMF. In addition, the N1 SMcontainer including a session accept message may further be sent to theAMF by invoking the service.

Step 1905. The AMF sends the received N2 SM information and the receivedN1 SM container to the master base station.

For example, the AMF sends an N2 session request to the master basestation, and the N2 session request includes the N2 SM information and aNAS message. The NAS message includes the PDU session identifier and theN1 SM container.

The N1 SM container includes the session accept message to be sent tothe UE. The session accept message includes a QoS rule. For example, theQoS rule includes a QoS rule identifier, the first service flowidentifier, the second service flow identifier, and a packet filter.

The N2 SM information includes at least the PDU session identifier andcore network tunnel information. The core network tunnel informationincludes first core network tunnel information and second core networktunnel information. For details, refer to the descriptions of FIG. 3Aand FIG. 3B. Details are not described herein again. The N2 SMinformation may further include a QoS parameter, a QFI-a, a QFI-b, sliceidentification information (for example, S-NSSAI), a session-AMBR, and aPDU session type. Optionally, the N2 SM information may further includea DNN.

Step 1906. The master base station initiates establishment of an accessnetwork resource between the master base station and the UE.

In other words, the master base station initiates establishment of afirst radio bearer between the master base station and the UE. Forexample, the first radio bearer is a DRB 1. In this step, the masterbase station sends identification information of the DRB 1 to the UE.The DRB 1 between the master base station and the UE is establishedthrough this step. In addition, in an embodiment, the master basestation further sends indication information to the UE using the ASlayer message.

The UE may receive the indication information using the AS layermessage. In the uplink direction, the UE may generate a first uplinkpacket and a second uplink packet based on the indication information,send the first uplink packet to the master base station over the firstradio bearer, and send the second uplink packet to the secondary basestation over a second radio bearer, where the first uplink packet andthe second uplink packet have a same first sequence number. For example,the indication information indicates the UE to replicate an uplinkpacket to obtain the first uplink packet and the second uplink packet,and send the first uplink packet and the second uplink packet overdifferent radio bearers.

For example, the UE determines, using the packet filter, packetscorresponding to the QFI-a and the QFI-b, replicates the packets basedon the indication information, and adds a same sequence number at theSDAP layer, to obtain the first uplink packet corresponding to the QFI-aand the second uplink packet corresponding to the QFI-b, and the UEsends, at the SDAP layer based on a correspondence between a QFI and aPDCP entity, the first uplink packet to a PDCP entity 1 and sends thesecond uplink packet to a PDCP entity 2, where the PDCP entity 1corresponds to the QFI-a, and the PDCP entity 2 corresponds to theQFI-b. Similarly, after the first uplink packet and the second uplinkpacket are processed at another protocol layer such as an RLC layer or aphysical layer, the first uplink packet is sent to the M-RAN over theDRB 1, and the second uplink packet is sent to the S-RAN over the DRB 2.The DRB 1 corresponds to the PDCP entity 1, and the DRB 2 corresponds tothe PDCP entity 2. After receiving the two uplink packets over the DRB 1and the DRB 2 respectively, the master base station and the secondarybase station add QFIs to the uplink packets based on a correspondencebetween a DRB and a QFI or based on QFIs carried in headers of theuplink packets. Specifically, the master base station adds the QFI-a tothe first uplink packet, the secondary base station adds the QFI-b tothe second uplink packet, and the master base station and the secondarybase station send the uplink packets to the UPF. Therefore, the UPFreceives the first uplink packet and the second uplink packet, and thefirst uplink packet and the second uplink packet respectively have theQFI-a and the QFI-b and have the same sequence number.

In other words, the first uplink packet sent by the UE corresponds tothe QFI-a, the second uplink packet corresponds to the QFI-b, and thefirst uplink packet and the second uplink packet have the same sequencenumber. The first uplink packet received by the UPF includes the QFI-a,the second uplink packet includes the QFI-b, and the first uplink packetand the second uplink packet have the same sequence number.

In a possible implementation, the indication information sent by the SMFto the UE may indicate that the first uplink packet corresponds to theQFI-a, and the second uplink packet corresponds to the QFI-b. In anotherpossible implementation, the UE may further add the QFI-a to the firstuplink packet and add the QFI-b to the second uplink packet at the SDAPlayer. Further, the indication information sent by the SMF to the UE mayindicate the UE to add the QFI-a to the first uplink packet and add theQFI-b to the second uplink packet.

In addition, in the downlink direction, when the UE receives a firstdownlink packet and a second downlink packet from the master basestation and the secondary base station respectively, where the firstdownlink packet and the second downlink packet have a same sequencenumber and respectively correspond to the QFI-a and the QFI-b, the UEdeduplicates the first downlink packet and the second downlink packetbased on the indication information. Therefore, further, optionally, theindication information sent by the SMF to the UE may further indicatethe UE to deduplicate the first downlink packet and the second downlinkpacket. The first downlink packet and the second downlink packet havethe same sequence number, and are respectively associated with the QFI-aand the QFI-b.

In another embodiment, the indication information may not be carried instep 1906, and the indication information may be sent to the UE in thefollowing step 1909. In still another embodiment, when the secondarybase station has an RRC function, the indication information mayalternatively be sent to the UE through the following step 1908′. Thisis not limited in this application.

Step 1907. The master base station determines to add the secondary basestation, and sends a secondary base station adding request to thesecondary base station.

Step 1908. The secondary base station returns a secondary base stationadding request acknowledgment to the master base station.

Step 1909. The master base station initiates RRC connectionreconfiguration to the UE.

In other words, the master base station initiates establishment of thesecond radio bearer between the secondary base station and the UE. Forexample, the second radio bearer is the DRB 2. In this step, thesecondary base station sends identification information of the DRB 2 tothe UE. The DRB 2 between the secondary base station and the UE isestablished through this step.

Step 1910. The master base station feeds back secondary base stationreconfiguration completion to the secondary base station, to notify thesecondary base station that the UE successfully completes the RRCconnection reconfiguration.

For step 1907 to step 1910, refer to the descriptions of step 1807 tostep 1810 in FIG. 18A and FIG. 18B. Details are not described hereinagain.

Optionally, if the secondary base station has the RRC function, theforegoing step 1908 to step 1910 may be replaced with the followingsteps.

1908′. The secondary base station initiates an RRC connectionestablishment process to the UE. For details, refer to the descriptionsof 1808′. Details are not described again.

1909′. The secondary base station returns a secondary base stationadding request acknowledgment to the master base station. For details,refer to the descriptions of step 1808. Details are not described again.

Step 1911. Random access procedure.

Step 1912. The master base station sends the first access network tunnelinformation and the second access network tunnel information to the AMF.Optionally, the master base station further sends, to the AMF, acorrespondence between the QFI-a and the first access network tunnelinformation and a correspondence between the QFI-b and the second accessnetwork tunnel information.

Step 1913. The AMF sends a context update request to the SMF, to forwardthe received N2 SM information to the SMF.

Step 1914. The SMF sends a forwarding rule to the UPF.

Step 1915. The SMF sends a context update response to the AMF.

For step 1912 to step 1915, refer to the descriptions of step 1812 tostep 1815 in FIG. 18A and FIG. 18B. Details are not described hereinagain.

Therefore, according to the packet transmission method in thisembodiment of the present disclosure, the uplink/downlink packets of thefirst service (for example, the URLLC service) may be transmittedthrough the two paths. Similarly, the method in this embodiment of thisapplication may further be used to transmit an uplink packet/a downlinkpacket of the first service through a plurality of (more than two)paths. Details are not described again. Therefore, reliability of packettransmission of the URLLC service is improved.

With reference to the descriptions of FIG. 18A, FIG. 18B, FIG. 19A, andFIG. 19B, an embodiment of this application provides a packettransmission method. As shown in FIG. 20, the method includes thefollowing steps.

Step 2001. UE obtains indication information from a network side device.

For example, if the network side device is an SMF, the UE may obtain theindication information from the SMF. Refer to step 1804 to step 1806 inFIG. 18A and FIG. 18B. Alternatively, if the network side device is abase station, the UE may obtain the indication information from themaster base station. For details, refer to step 1906 in FIG. 19A andFIG. 19B. Details are not described again. For example, the indicationinformation indicates the UE to replicate an uplink packet to obtain afirst uplink packet and a second uplink packet, and send the firstuplink packet and the second uplink packet over different radio bearers.The first uplink packet and the second uplink packet have a samesequence number.

Step 2002. The UE generates the first uplink packet and the seconduplink packet based on the indication information, sends the firstuplink packet to a first base station over a first radio bearer, andsends the second uplink packet to a second base station over a secondradio bearer, where the first uplink packet and the second uplink packethave the same sequence number, and the first uplink packet correspondsto a first service flow identifier, and the second uplink packetcorresponds to a second service flow identifier.

For example, the first base station may be the master base station inFIG. 18A, FIG. 18B, FIG. 19A, or FIG. 19B, the second base station maybe the secondary base station in FIG. 18A, FIG. 18B, FIG. 19A, or FIG.19B, the first radio bearer may be the DRB 1 in FIG. 18A, FIG. 18B, FIG.19A, or FIG. 19B, and the second radio bearer may be the DRB 2 in FIG.18A, FIG. 18B, FIG. 19A, or FIG. 19B.

For example, the UE replicates a packet at a first protocol layer basedon the indication information, to obtain the first uplink packet and thesecond uplink packet. For example, if the first protocol layer includesan HRP layer, the UE obtains the indication information from the SMFusing an NAS message. Refer to the descriptions of FIG. 18A and FIG.18B. Alternatively, if the first protocol layer includes an SDAP layer,the UE obtains the indication information from the base station using anAS message. Refer to the descriptions of FIG. 19A and FIG. 19B.

Optionally, the UE may add the first service flow identifier to thefirst uplink packet, and add the second service flow identifier to thesecond uplink packet. In other words, the first uplink packet includesthe first service flow identifier, and the second uplink packet includesthe second service flow identifier. Further, optionally, the indicationinformation further indicates the UE to add the first service flowidentifier to the first uplink packet and add the second service flowidentifier to the second uplink packet.

In addition, in a downlink direction, the UE receives a first downlinkpacket and a second downlink packet from the first base station and thesecond base station respectively, where the first downlink packet has asecond sequence number and corresponds to the first service flowidentifier, and the second downlink packet has the second sequencenumber and corresponds to the second service flow identifier. The UEdeduplicates the first downlink packet and the second downlink packetbased on the indication information.

Optionally, the indication information further indicates the UE todeduplicate the two downlink packets that have the same sequence numberand that respectively have the first service flow identifier and thesecond service flow identifier.

It should be noted that, an operation in the downlink direction does notdepend on an uplink solution. In other words, an operation on a downlinkside of the UE may also constitute an independent solution.

Similarly, the method in this embodiment of this application may furtherbe used to transmit an uplink packet/a downlink packet of a firstservice through a plurality of (more than two) paths. Details are notdescribed again. Therefore, reliability of packet transmission of aURLLC service is improved.

With reference to the descriptions of FIG. 18A, FIG. 18B, FIG. 19A, andFIG. 19B, an embodiment of this application provides a packettransmission method. As shown in FIG. 21, the method includes thefollowing steps.

Step 2101. A UPF network element receives an uplink forwarding rule froma SMF network element. For example, the uplink forwarding rule indicatesthe UPF network element to deduplicate two uplink packets that have asame sequence number and that respectively have a first service flowidentifier and a second service flow identifier.

For example, the UPF network element may be the UPF in FIG. 18A, FIG.18B, FIG. 19A, or FIG. 19B, and the SMF network element may be the SMFin FIG. 18A, FIG. 18B, FIG. 19A, or FIG. 19B. For step 2101, refer tothe descriptions of step 1814 in FIG. 18A and FIG. 18B or step 1914 inFIG. 19A and FIG. 19B. Details are not described again.

Step 2102. The UPF network element receives a first uplink packet and asecond uplink packet, where the first uplink packet has the firstservice flow identifier and a first sequence number, and the seconduplink packet has the second service flow identifier and the firstsequence number.

Step 2103. The UPF network element deduplicates the first uplink packetand the second uplink packet according to the uplink forwarding rule.

In addition, in a downlink direction, the UPF network element receives adownlink forwarding rule from the SMF network element, generates a firstdownlink packet and a second downlink packet according to the downlinkforwarding rule, sends the first downlink packet to a first basestation, and sends the second downlink packet to a second base station,where the first downlink packet has the first service flow identifierand a second sequence number, and the second downlink packet has thesecond service flow identifier and the second sequence number.

Optionally, the generating, by the UPF network element, a first downlinkpacket and a second downlink packet according to the downlink forwardingrule includes replicating, by the UPF network element, a packet at afirst protocol layer according to the downlink forwarding rule, toobtain the first downlink packet and the second downlink packet, wherethe first protocol layer includes an HRP layer or a GTP-U layer.

It should be noted that, an operation in the downlink direction does notdepend on an uplink solution. In other words, an operation on a downlinkside of the UPF may also constitute an independent solution.

Similarly, the method in this embodiment of this application may furtherbe used to transmit an uplink packet/a downlink packet of a firstservice through a plurality of (more than two) paths. Details are notdescribed again. Therefore, reliability of packet transmission of aURLLC service is improved.

With reference to the descriptions of FIG. 3A, FIG. 3B, and FIG. 5, anembodiment of this application provides a packet transmission method. Asshown in FIG. 6, the method includes the following steps.

Step 601. An SMF network element receives first access network tunnelinformation and second access network tunnel information that correspondto a first service.

For example, the SMF network element may be the SMF in FIG. 3A, FIG. 3B,or FIG. 5.

For example, after receiving N2 SM information including the firstaccess network tunnel information and the second access network tunnelinformation, an access and mobility management network element forwardsthe N2 SM information to the SMF network element. Specifically, for step601, refer to the descriptions of step 311 and step 312 in FIG. 3A andFIG. 3B or the descriptions of step 507 and step 508 in FIG. 5. Detailsare not described herein again.

Step 602. The SMF network element sends a downlink forwarding rule to aUPF network element, where the downlink forwarding rule includes thefirst access network tunnel information and the second access networktunnel information, and the downlink forwarding rule indicates the UPFnetwork element to replicate a received downlink packet of the firstservice, and send downlink packets of the first service through twopaths respectively corresponding to the first access network tunnelinformation and the second access network tunnel information.

For example, the UPF network element may be the UPF in FIG. 3A, FIG. 3B,or FIG. 5. For example, in a dual connectivity scenario, the two pathsmay be a first path between the UPF network element and a master basestation, and a second path between the UPF network element and asecondary base station. In a single connectivity scenario, the two pathsmay be a first path and a second path between the UPF network elementand a base station.

For step 602, refer to the descriptions of step 313 in FIG. 3A and FIG.3B or step 509 in FIG. 5. Details are not described herein again.

According to the foregoing method, for a specific first service (forexample, a URLLC service requiring high reliability), the SMF networkelement sends, to the UPF network element, the downlink forwarding ruleincluding the first access network tunnel information and the secondaccess network tunnel information such that after subsequently receivinga downlink packet of the first service, the UPF network elementreplicates the downlink packet of the first service, and sends downlinkpackets of the first service through the two paths respectivelycorresponding to the first access network tunnel information and thesecond access network tunnel information. In this way, reliability ofpacket transmission of the first service is improved.

Similarly, the method in this embodiment of this application may furtherbe used to transmit an uplink packet/a downlink packet of the firstservice through a plurality of (more than two) paths. Details are notdescribed again. Therefore, reliability of packet transmission of theURLLC service is improved.

Optionally, if the first service is at a service flow granularity, thedownlink forwarding rule further includes a service flow identifier ofthe first service and a session identifier, or if the first service isat a session granularity, the downlink forwarding rule further includesa session identifier of the first service. Therefore, for services atdifferent granularities, downlink forwarding rules for correspondinggranularities may be provided such that the UPF network element canimplement more accurate and efficient packet transmission.

Optionally, the method further includes sending, by the SMF networkelement, indication information to a base station, where the indicationinformation triggers determining of the first access network tunnelinformation and the second access network tunnel information. In otherwords, after receiving the indication information, the base stationlearns that the first access network tunnel information and the secondaccess network tunnel information need to be determined. For example,the indication information may include at least one of the following aQoS parameter, slice identification information, a DN name, and firstcore network tunnel information and second core network tunnelinformation. The QoS parameter includes at least one of a 5QI and a QFI.The base station that receives the indication information herein may bethe master base station in the dual connectivity scenario or the basestation in the single connectivity scenario.

Optionally, the method further includes sending, by the SMF networkelement, an uplink forwarding rule to the base station, where the uplinkforwarding rule includes the first core network tunnel information andthe second core network tunnel information, and the uplink forwardingrule indicates the base station to replicate a received uplink packet ofthe first service, and send uplink packets of the first service to theUPF network element through two paths respectively corresponding to thefirst core network tunnel information and the second core network tunnelinformation. The base station herein is the base station in the singleconnectivity scenario.

Similarly, if the first service is at the service flow granularity, theuplink forwarding rule further includes the service flow identifier ofthe first service and the session identifier, or the first service is atthe session granularity, the uplink forwarding rule further includes thesession identifier of the first service.

Optionally, the method further includes allocating, by the SMF networkelement, a first service flow identifier and a second service flowidentifier to the first service, and sending the first service flowidentifier and the second service flow identifier to UE. Refer to thedescriptions of step 1803 in FIG. 18A and FIG. 18B or step 1903 in FIG.19A and FIG. 19B. Details are not described again.

Optionally, the method further includes sending, by the SMF networkelement, the uplink forwarding rule to the UPF network element, wherethe uplink forwarding rule indicates the UPF network element todeduplicate two uplink packets that have a same sequence number and thatrespectively have the first service flow identifier and the secondservice flow identifier. Refer to the descriptions of step 1814 in FIG.18A and FIG. 18B or step 1914 in FIG. 19A and FIG. 19B. Details are notdescribed again.

Optionally, the method further includes sending, by the SMF networkelement, indication information to the UE using a NAS message, where theindication information indicates the UE to replicate an uplink packet toobtain a first uplink packet and a second uplink packet, and send thefirst uplink packet and the second uplink packet over different radiobearers, where the first uplink packet and the second uplink packet havea same sequence number. Further, optionally, the indication informationfurther indicates that the first uplink packet corresponds to a QFI-a,and the second uplink packet corresponds to a QFI-b. For details, referto the descriptions of step 1804 to step 1806 in FIG. 18A and FIG. 18B.Details are not described again.

Optionally, the method further includes adding, by the UE, the firstservice flow identifier to the first uplink packet (for example, at anHRP layer), and adding the second service flow identifier to the seconduplink packet. For example, the indication information further indicatesthe UE to add the first service flow identifier to the first uplinkpacket and add the second service flow identifier to the second uplinkpacket.

Optionally, the downlink packets of the first service that are sentthrough the two paths respectively corresponding to the first accessnetwork tunnel information and the second access network tunnelinformation include a first downlink packet and a second downlinkpacket, where the first downlink packet and the second downlink packetinclude a same first sequence number. The first downlink packetcorresponds to the first service flow identifier, and the seconddownlink packet corresponds to the second service flow identifier.Optionally, the first downlink packet sent by the UE includes the firstservice flow identifier, and the second downlink packet includes thesecond service flow identifier. Refer to the descriptions of FIG. 18A,FIG. 18B, FIG. 19A, or FIG. 19B. Details are not described again.

Optionally, the indication information further indicates the UE todeduplicate the first downlink packet and the second downlink packet.The first downlink packet and the second downlink packet have the samesequence number, and are respectively associated with the first serviceflow identifier and the second service flow identifier.

An embodiment of this application further provides a packet transmissionmethod. As shown in FIG. 7, the method includes the following steps.

Step 701. A base station determines first access network tunnelinformation and second access network tunnel information that correspondto a first service.

For example, the base station may be the master base station in FIG. 3Aand FIG. 3B or the base station in FIG. 5.

For step 701, refer to the descriptions of step 306 and step 307 in FIG.3A and FIG. 3B or step 506 in FIG. 5. Details are not described hereinagain.

Step 702. The base station sends the first access network tunnelinformation and the second access network tunnel information to an SMFnetwork element, where the first access network tunnel information andthe second access network tunnel information are used for determinationof a downlink forwarding rule, and the downlink forwarding ruleindicates a UPF network element to replicate a received downlink packetof the first service, and send downlink packets of the first servicethrough two paths respectively corresponding to the first access networktunnel information and the second access network tunnel information.

For example, the SMF network element may be the SMF in FIG. 3A, FIG. 3B,or FIG. 5. In a dual connectivity scenario, the two paths may be a firstpath between the UPF network element and a master base station, and asecond path between the UPF network element and a secondary basestation. In a single connectivity scenario, the two paths may be a firstpath and a second path between the UPF network element and the basestation.

For step 702, refer to the descriptions of step 311 and step 312 in FIG.3A and FIG. 3B or step 507 and step 508 in FIG. 5. Details are notdescribed herein again.

According to the foregoing method, the base station sends the firstaccess network tunnel information and the second access network tunnelinformation to the SMF network element. For a specific first service(for example, a URLLC service requiring high reliability), the SMFnetwork element sends, to the UPF network element, the downlinkforwarding rule including the first access network tunnel informationand the second access network tunnel information such that aftersubsequently receiving a downlink packet of the first service, the UPFnetwork element replicates the downlink packet of the first service, andsends downlink packets of the first service through the two pathsrespectively corresponding to the first access network tunnelinformation and the second access network tunnel information. In thisway, reliability of packet transmission of the first service isimproved.

Similarly, the method in this embodiment of this application may furtherbe used to transmit an uplink packet/a downlink packet of the firstservice through a plurality of (more than two) paths. Details are notdescribed again. Therefore, reliability of packet transmission of theURLLC service is improved.

Optionally, if the first service is at a service flow granularity, thedownlink forwarding rule further includes a service flow identifier ofthe first service and a session identifier, or if the first service isat a session granularity, the downlink forwarding rule further includesa session identifier of the first service. Therefore, for services atdifferent granularities, downlink forwarding rules for correspondinggranularities may be provided such that the UPF network element canimplement more accurate and efficient packet transmission.

Optionally, the method further includes receiving, by the base station,indication information from the SMF network element, where theindication information triggers determining of the first access networktunnel information and the second access network tunnel information.Step 701 includes determining, by the base station, the first accessnetwork tunnel information and the second access network tunnelinformation based on the indication information. In other words, afterreceiving the indication information, the base station learns that thefirst access network tunnel information and the second access networktunnel information need to be determined. For example, the indicationinformation may include at least one of the following a QoS parameter,slice identification information, a DN name, and first core networktunnel information and second core network tunnel information. The QoSparameter includes at least one of a 5QI and a QFI.

Optionally, the method further includes receiving, by the base station,an uplink forwarding rule from the SMF network element, where the uplinkforwarding rule includes the first core network tunnel information andthe second core network tunnel information, and replicating, by the basestation, a received uplink packet of the first service according to theuplink forwarding rule, and sending uplink packets of the first serviceto the UPF network element through two paths respectively correspondingto the first core network tunnel information and the second core networktunnel information. The base station herein is the base station in thesingle connectivity scenario.

Similarly, if the first service is at the service flow granularity, theuplink forwarding rule further includes the service flow identifier ofthe first service and the session identifier, or if the first service isat the session granularity, the uplink forwarding rule further includesthe session identifier of the first service.

Optionally, the method further includes sending, by the base station,indication information to UE using an AS message, where the indicationinformation indicates the UE to replicate an uplink packet to obtain afirst uplink packet and a second uplink packet, and send the firstuplink packet and the second uplink packet over different radio bearers,and the first uplink packet and the second uplink packet have a samesequence number. Further, optionally, the indication information furtherindicates that the first uplink packet corresponds to a QFI-a, and thesecond uplink packet corresponds to a QFI-b. Refer to the descriptionsof step 1906 in FIG. 19A and FIG. 19B. Details are not described again.

Optionally, the method further includes sending, by the base station tothe SMF network element, a first service flow identifier correspondingto the first access network tunnel information and a second service flowidentifier corresponding to the second access network tunnelinformation.

Optionally, the method further includes indicating, by the base station,the UE to add a service flow identifier to the first uplink packet.

Optionally, the method further includes, when the base stationdetermines to transmit a packet in a dual connectivity manner,indicating, by the base station, the UE to generate two second uplinkpackets, where the two second uplink packets have a same sequence numberand a same service flow identifier.

Optionally, the method further includes indicating, by the base station,the UE to deduplicate received downlink packets that have a samesequence number and a same service flow identifier. For example, in adual connectivity (or dual base station) downlink scenario, the basestation indicates the UE to deduplicate received downlink packets thathave a same sequence number and a same service flow identifier.

Optionally, the method further includes receiving, by the base station,the downlink packets of the first service through the two pathsrespectively corresponding to the first access network tunnelinformation and the second access network tunnel information, anddeduplicating the downlink packets that have the same sequence numberand service flow identifier. For example, in a single connectivity (orsingle base station) downlink scenario, the base station deduplicatesthe downlink packets that have a same sequence number and a same serviceflow identifier.

With reference to the descriptions of FIG. 3A, FIG. 3B, FIG. 5, FIG.12A, and FIG. 12B, an embodiment of this application further provides apacket transmission method. As shown in FIG. 13, the method includes thefollowing steps.

Step 1301. A base station obtains a first indication.

The first indication includes capability information or indicationinformation that is from a session management network element.

For example, the indication information indicates the base station toindicate the UE to add a service flow identifier to an uplink packet ofa first session or an uplink packet of a first service flow of a firstsession.

The capability information indicates at least one of the following,whether the base station (namely, the master base station) has acapability of transmitting or receiving a packet in a dual connectivitymanner, whether a neighboring base station (namely, a base station, forexample, the secondary base station, having an Xn interface with thebase station) of the base station has the capability of transmitting orreceiving a packet in the dual connectivity manner, and whether anotherbase station (for example, the secondary base station) that has thecapability of transmitting or receiving a packet in the dualconnectivity manner is deployed in a slice associated with the basestation.

Step 1302. The base station indicates, according to the firstindication, the UE to add a service flow identifier to a first uplinkpacket.

The service flow identifier may include at least one of a sessionidentifier, a QFI, and a 5-tuple.

For example, when the first indication includes the indicationinformation, the base station indicates, based on the receivedindication information, the UE to add the service flow identifier to thefirst uplink packet.

When the first indication includes the capability information, theindicating, by the base station according to the first indication, theUE to add a service flow identifier to a first uplink packet includes,when the capability information meets a first condition, indicating, bythe base station, the UE to add the service flow identifier to the firstuplink packet, where the first condition includes at least one of thefollowing the capability information indicates that the base station hasthe capability of transmitting or receiving a packet in the dualconnectivity manner, the capability information indicates that theneighboring base station of the base station has the capability oftransmitting or receiving a packet in the dual connectivity manner, andthe capability information indicates that the other base station havingthe capability of transmitting or receiving a packet in the dualconnectivity manner is deployed in the slice associated with the basestation.

For example, for step 1301 and step 1302, refer to the descriptions ofFIG. 3A and FIG. 3B. Details are not described herein again.

Therefore, when the dual connectivity manner is used or the dualconnectivity manner may be used subsequently, the base station indicatesthe UE to add the service flow identifier to the uplink packet. In thisway, for the UE, a same protocol stack format is used for the singleconnectivity manner and the dual connectivity manner. After the UE issubsequently switched to the dual connectivity manner, the UE maydirectly perform processing based on the protocol stack format, to avoidcomplex operations and signaling exchanges, and reduce a latency,thereby improving user experience.

Optionally, the method further includes, when the base stationdetermines to transmit or receive a packet in the dual connectivitymanner, indicating, by the base station, the UE to generate two seconduplink packets, where the two second uplink packets have a same sequencenumber and a same service flow identifier.

Optionally, the method further includes indicating, by the base station,the UE to deduplicate received downlink packets that have a samesequence number and a same service flow identifier. For example, in adual connectivity (or dual base station) downlink scenario, the basestation indicates the UE to deduplicate received downlink packets thathave a same sequence number and a same service flow identifier.

Optionally, the method further includes receiving, by the base station,downlink packets of a first service through the two paths respectivelycorresponding to the first access network tunnel information and thesecond access network tunnel information, and deduplicating downlinkpackets that have a same sequence number and a same service flowidentifier. For example, in a single connectivity (or single basestation) downlink scenario, the base station deduplicates downlinkpackets that have a same sequence number and a same service flowidentifier. For this step, refer to the descriptions of step 1212 inFIG. 12A and FIG. 12B.

With reference to the descriptions of FIG. 3A, FIG. 3B, FIG. 11A, andFIG. 11B, an embodiment of this application further provides a packettransmission method. This method is applicable to a dual connectivityscenario. As shown in FIG. 14, the method includes the following steps.

Step 1401. UE generates a first uplink packet and a second uplink packetaccording to an indication obtained from a first base station, where thefirst uplink packet and the second uplink packet have a same firstservice flow identifier and a same first sequence number.

Step 1402. The UE sends the first uplink packet to the first basestation, and sends the second uplink packet to a second base station.

For step 1401 and step 1402, refer to the descriptions of step 1101 inFIG. 3A, FIG. 3B, FIG. 11A, and FIG. 11B.

Therefore, for a dual connectivity manner, the UE adds the service flowidentifier and the sequence number to the uplink packet according to theindication of the base station. For a packet of a specific service (forexample, a URLLC service requiring high reliability), the UE replicatesa packet. In this way, reliability of packet transmission of thespecific service is improved.

Optionally, the method further includes receiving, by the UE, a firstdownlink packet and a second downlink packet from the first base stationand the second base station respectively, where the first downlinkpacket and the second downlink packet include a same second service flowidentifier and a same second sequence number, and deduplicating, by theUE, the first downlink packet and the second downlink packet accordingto the indication of the base station. For this step, refer to thedescriptions of step 1113 in FIG. 11A and FIG. 11B.

In the foregoing embodiments provided in this application, the solutionsof the communication methods provided in the embodiments of thisapplication are separately described from a perspective of each networkelement and from a perspective of interaction between the networkelements. It may be understood that, to implement the foregoingfunctions, each of the network elements, for example, the foregoing SMFnetwork element and the base station, includes a corresponding hardwarestructure and/or software module for performing each function. A personskilled in the art should easily be aware that, in combination withunits and algorithm steps of the examples described in the embodimentsdisclosed in this specification, this application may be implemented byhardware or a combination of hardware and computer software. Whether afunction is performed by hardware or hardware driven by computersoftware depends on particular applications and design constraints ofthe technical solutions. A person skilled in the art may use differentmethods to implement the described functions for each particularapplication, but it should not be considered that the implementationgoes beyond the scope of this application.

For example, when the network element implements a correspondingfunction using a software module, a packet transmission apparatus mayinclude a receiving module 801 and a sending module 802, as shown inFIG. 8. The apparatus may be an SMF network element or a chip.

The apparatus may be configured to perform an operation of the SMF inFIG. 3A, FIG. 3B, FIG. 5, FIG. 18A, FIG. 18B, FIG. 19A, or FIG. 19B, orthe SMF network element in FIG. 6. For example, the receiving module 801is configured to receive first access network tunnel information andsecond access network tunnel information that correspond to a firstservice. The sending module is configured to send a downlink forwardingrule to a UPF network element, where the downlink forwarding ruleincludes the first access network tunnel information and the secondaccess network tunnel information, and the downlink forwarding ruleindicates the UPF network element to replicate a received downlinkpacket of the first service, and send downlink packets of the firstservice through two paths respectively corresponding to the first accessnetwork tunnel information and the second access network tunnelinformation.

Therefore, for a specific first service (for example, a URLLC servicerequiring high reliability), the SMF network element sends, to the UPFnetwork element, the downlink forwarding rule including the first accessnetwork tunnel information and the second access network tunnelinformation such that after subsequently receiving a downlink packet ofthe first service, the UPF network element replicates the downlinkpacket of the first service, and sends downlink packets of the firstservice through the two paths respectively corresponding to the firstaccess network tunnel information and the second access network tunnelinformation. In this way, reliability of packet transmission of thefirst service is improved.

Optionally, if the first service is at a service flow granularity, thedownlink forwarding rule further includes a service flow identifier ofthe first service and a session identifier, or if the first service isat a session granularity, the downlink forwarding rule further includesa session identifier of the first service.

Optionally, the sending module 802 is further configured to sendindication information to a base station, where the indicationinformation triggers determining of the first access network tunnelinformation and the second access network tunnel information. Forexample, the indication information includes at least one of thefollowing a QoS parameter, slice identification information, a DN name,and first core network tunnel information and second core network tunnelinformation.

Optionally, the sending module 802 is configured to send an uplinkforwarding rule to the base station, where the uplink forwarding ruleincludes the first core network tunnel information and the second corenetwork tunnel information, and the uplink forwarding rule indicates thebase station to replicate a received uplink packet of the first service,and send uplink packets of the first service to the UPF network elementthrough two paths respectively corresponding to the first core networktunnel information and the second core network tunnel information.Further, optionally, if the first service is at the service flowgranularity, the uplink forwarding rule further includes the serviceflow identifier of the first service and the session identifier, or ifthe first service is at the session granularity, the uplink forwardingrule further includes the session identifier of the first service.

Optionally, the downlink packets of the first service that are sentthrough the two paths respectively corresponding to the first accessnetwork tunnel information and the second access network tunnelinformation include a first downlink packet and a second downlinkpacket, where the first downlink packet and the second downlink packethave a same sequence number, the first downlink packet further includesa first service flow identifier, and the second downlink packet furtherincludes a second service flow identifier.

Optionally, the sending module 802 is further configured to send anuplink forwarding rule to the UPF network element, where the uplinkforwarding rule indicates the UPF network element to deduplicate twouplink packets that have a same sequence number and that respectivelyhave the first service flow identifier and the second service flowidentifier.

Optionally, the sending module 802 is further configured to sendindication information to UE using a NAS message, where the indicationinformation indicates the UE to replicate an uplink packet to obtain afirst uplink packet and a second uplink packet, and send the firstuplink packet and the second uplink packet over different radio bearers,where the first uplink packet and the second uplink packet have a samesequence number. For example, the first uplink packet corresponds to thefirst service flow identifier, and the second uplink packet correspondsto the second service flow identifier.

The apparatus may further include a processing module 803. For example,the processing module 803 is configured to allocate the first serviceflow identifier and the second service flow identifier to the firstservice, and send the first service flow identifier and the secondservice flow identifier to the UE. The receiving module 801, the sendingmodule 802, and the processing module 803 in the apparatus may furtherimplement another operation or function of the SMF or the SMF networkelement in the foregoing method. Details are not described herein again.

As shown in FIG. 9, another packet transmission apparatus may include aprocessing module 901 and a sending module 902. Optionally, theapparatus further includes a receiving module 903.

In an embodiment, the apparatus may be a base station or a chip. Theapparatus may be configured to perform an operation of the master basestation in FIG. 3A, FIG. 3B, FIG. 18A, FIG. 18B, FIG. 19A, or FIG. 19B,or the base station in FIG. 5 or FIG. 7. For example, the processingmodule 901 is configured to determine first access network tunnelinformation and second access network tunnel information that correspondto a first service. The sending module 902 is configured to send thefirst access network tunnel information and the second access networktunnel information to an SMF network element, where the first accessnetwork tunnel information and the second access network tunnelinformation are usable for determination of a downlink forwarding rule,and the downlink forwarding rule indicates a UPF network element toreplicate a received downlink packet of the first service, and senddownlink packets of the first service through two paths respectivelycorresponding to the first access network tunnel information and thesecond access network tunnel information.

Therefore, the base station sends the first access network tunnelinformation and the second access network tunnel information to the SMFnetwork element. For a specific first service (for example, a URLLCservice requiring high reliability), the SMF network element sends, tothe UPF network element, the downlink forwarding rule including thefirst access network tunnel information and the second access networktunnel information such that after subsequently receiving a downlinkpacket of the first service, the UPF network element replicates thedownlink packet of the first service, and sends downlink packets of thefirst service through the two paths respectively corresponding to thefirst access network tunnel information and the second access networktunnel information. In this way, reliability of packet transmission ofthe first service is improved.

Optionally, if the first service is at a service flow granularity, thedownlink forwarding rule further includes a service flow identifier ofthe first service and a session identifier, or if the first service isat a session granularity, the downlink forwarding rule further includesa session identifier of the first service.

Optionally, the receiving module 903 is configured to, before theprocessing module 901 determines the first access network tunnelinformation and the second access network tunnel information thatcorrespond to the first service, receive indication information from theSMF network element, where the indication information triggers the basestation to determine the first access network tunnel information and thesecond access network tunnel information. The processing module 901 isconfigured to determine the first access network tunnel information andthe second access network tunnel information based on the indicationinformation. For example, the indication information includes at leastone of the following a QoS parameter, slice identification information,a DN name, and first core network tunnel information and second corenetwork tunnel information.

Optionally, the receiving module 903 is configured to receive an uplinkforwarding rule from the SMF network element, where the uplinkforwarding rule includes the first core network tunnel information andthe second core network tunnel information. The processing module 901 isconfigured to replicate a received uplink packet of the first serviceaccording to the uplink forwarding rule, and the sending module 902 isconfigured to send uplink packets of the first service to the UPFnetwork element through two paths respectively corresponding to thefirst core network tunnel information and the second core network tunnelinformation. Further, optionally, if the first service is at the serviceflow granularity, the uplink forwarding rule further includes theservice flow identifier of the first service and the session identifier,or if the first service is at the session granularity, the uplinkforwarding rule further includes the session identifier of the firstservice.

Optionally, the sending module 902 is further configured to sendindication information to UE using an AS message, where the indicationinformation indicates the UE to replicate an uplink packet to obtain afirst uplink packet and a second uplink packet, and send the firstuplink packet and the second uplink packet over different radio bearers.

In another embodiment, the processing module 901 is configured tocontrol the sending module 902 to initiate establishment of a firstradio bearer between a first base station and the UE. In a process ofestablishing a second radio bearer between a second base station and theUE, the sending module 902 or a sending module in the second basestation sends indication information to the UE, where the indicationinformation indicates the UE to associate the first radio bearer and thesecond radio bearer with a same PDCP entity on the UE. For example, thefirst base station or the second base station sends the indicationinformation to the UE using a RRC layer message.

In addition, the processing module 901, the sending module 902, and thereceiving module 903 in the apparatus may further implement anotheroperation or function of the base station or the master base station(for example, in FIG. 11A, FIG. 11B, FIG. 12A, FIG. 12B, or FIG. 13) inthe foregoing method. Details are not described herein again.

In another embodiment, the apparatus may be UE or a chip. The apparatusmay be configured to perform an operation of the UE in FIG. 11A, FIG.11B, FIG. 15A, FIG. 15B, FIG. 17, FIG. 18A, FIG. 18B, FIG. 19A, FIG.19B, or FIG. 20. For example, the processing module 901 is configured togenerate a first uplink packet and a second uplink packet according toan indication obtained from a first base station, where the first uplinkpacket and the second uplink packet have a same first service flowidentifier and a same first sequence number. The sending module 902 isconfigured to send the first uplink packet to the first base station,and send the second uplink packet to a second base station.

Therefore, for a dual connectivity manner, the UE adds the service flowidentifier and the sequence number to the uplink packet according to theindication of the base station. For a packet of a specific service (forexample, a URLLC service requiring high reliability), the UE replicatesa packet. In this way, reliability of packet transmission of thespecific service is improved.

Optionally, the receiving module 903 is configured to receive a firstdownlink packet and a second downlink packet from the first base stationand the second base station respectively, where the first downlinkpacket and the second downlink packet include a same second service flowidentifier and a same second sequence number. The processing module 901is further configured to deduplicate the first downlink packet and thesecond downlink packet according to the indication of the base station.

For another example, the sending module 902 and/or the receiving module903 are/is configured to interact with a first base station, toestablish a first radio bearer between the first base station and UE. Ina process of establishing a second radio bearer between a second basestation and the UE, the receiving module 903 is configured to receiveindication information from the first base station or the second basestation, where the indication information indicates the UE to associatethe first radio bearer and the second radio bearer with a same PDCPentity on the UE. The processing module 901 is configured to generate afirst packet and a second packet based on the indication information,where the first packet and the second packet have a same sequencenumber. The sending module 902 is configured to send the first packet tothe first base station over the first radio bearer, and send the secondpacket to the second base station over the second radio bearer. Forexample, the generating, by the UE, a first packet and a second packetbased on the indication information includes replicating, by the UE, apacket at a PDCP layer based on the indication information, to obtainthe first packet and the second packet.

Alternatively, for another example, the receiving module 903 isconfigured to obtain indication information from a network side device,and the processing module 901 is configured to generate a first uplinkpacket and a second uplink packet based on the indication information,send the first uplink packet to a first base station over a first radiobearer, and send the second uplink packet to a second base station overa second radio bearer, where the first uplink packet and the seconduplink packet have a same sequence number. The first uplink packetcorresponds to a first service flow identifier, and the second uplinkpacket corresponds to a second service flow identifier.

Optionally, the generating, by the UE, a first uplink packet and asecond uplink packet based on the indication information includesreplicating, by the UE, a packet at a first protocol layer based on theindication information, to obtain the first uplink packet and the seconduplink packet. For example, the first protocol layer includes a HRPlayer, and the UE obtains the indication information from an SMF networkelement using a NAS message, or the first protocol layer includes a SDAPlayer, and the UE obtains the indication information from the first basestation using an AS message.

Optionally, the receiving module 903 is further configured to receive afirst downlink packet and a second downlink packet from the first basestation and the second base station respectively, where the firstdownlink packet has a second sequence number and corresponds to thefirst service flow identifier, and the second downlink packet has thesecond sequence number and corresponds to the second service flowidentifier, and the processing module 901 is further configured todeduplicate the first downlink packet and the second downlink packetbased on the indication information.

In another embodiment, the apparatus may be a UPF or a chip. Theapparatus may be configured to perform an operation of the UPF in FIG.18A, FIG. 18B, FIG. 19A, FIG. 19B, FIG. 20, or FIG. 21. For example, thereceiving module 903 is configured to receive an uplink forwarding rulefrom an SMF network element, and receive a first uplink packet and asecond uplink packet, where the first uplink packet has a first serviceflow identifier and a first sequence number, and the second uplinkpacket has a second service flow identifier and the first sequencenumber, and the processing module 901 is configured to deduplicate thefirst uplink packet and the second uplink packet according to the uplinkforwarding rule.

Optionally, the uplink forwarding rule indicates a UPF network elementto deduplicate the two uplink packets that have the same sequence numberand that respectively have the first service flow identifier and thesecond service flow identifier.

Optionally, the receiving module 903 is further configured to receive adownlink forwarding rule from the SMF network element, the processingmodule 901 is further configured to generate a first downlink packet anda second downlink packet according to the downlink forwarding rule, andthe sending module 902 is configured to send the first downlink packetto a first base station, and send the second downlink packet to a secondbase station, where the first downlink packet has the first service flowidentifier and a second sequence number, the second downlink packet hasthe second service flow identifier and the second sequence number. Forexample, to generate the first downlink packet and the second downlinkpacket according to the downlink forwarding rule, the processing module901 is configured to replicate a packet at a first protocol layeraccording to the downlink forwarding rule, to obtain the first downlinkpacket and the second downlink packet, where the first protocol layerincludes a HRP layer or a GTP-U layer.

FIG. 10 is another possible schematic structural diagram of the packettransmission apparatus in the foregoing embodiment. The apparatusincludes a transceiver 1001 and a processor 1002, as shown in FIG. 10.

For example, the processor 1002 may be a general-purpose microprocessor,a data processing circuit, an application-specific integrated circuit(ASIC), or a field-programmable gate array (FPGA) circuit. The apparatusmay further include a memory 1003. For example, the memory is arandom-access memory (RAM). The memory is configured to couple to theprocessor 1002, and store a computer program 10031 necessary for theapparatus.

In addition, the communication method in the foregoing embodimentfurther provides a computer-readable storage medium 1004 (for example, ahard disk). The computer-readable storage medium stores a computerprogram 10041 of the foregoing apparatus, and the computer program 10041may be loaded into the processor 1002.

When the computer program 10031 or 10041 is run on a computer (forexample, the processor 1002), the computer may be enabled to perform theforegoing method.

For example, in an embodiment, the processor 1002 is configured toperform an operation or a function of the SMF network element (forexample, an SMF). The transceiver 1004 is configured to implementcommunication between the apparatus and a UPF network element, a basestation (or a master base station), or another CP network element (forexample, an AMF).

In another embodiment, the processor 1002 is configured to perform anoperation or a function of the base station (or the master basestation). The transceiver 1004 is configured to implement communicationbetween the apparatus and a UPF network element and between theapparatus and an SMF network element (for example, an SMF).

In still another embodiment, the processor 1002 is configured to performan operation or a function of the UE. The transceiver 1004 is configuredto implement communication between the apparatus and a base station andbetween the apparatus and a UPF network element.

In still another embodiment, the processor 1002 is configured to performan operation or a function of the UPF. The transceiver 1004 isconfigured to implement communication between the apparatus and a basestation and between the apparatus and an SMF network element.

The processor that is of the packet transmission apparatus and that isconfigured to perform this application may be a central processing unit(CPU), a general-purpose processor, a digital signal processor (DSP), anASIC, a FPGA or another programmable logical device, a transistorlogical device, a hardware component, or any combination thereof. Theprocessor may implement or execute various example logical blocks,modules, and circuits described with reference to content disclosed inthis application. The processor may be a combination of one or moreprocessors implementing a computing function, for example, a combinationof one or more microprocessors, or a combination of a DSP and amicroprocessor.

Method or algorithm steps described in combination with the contentdisclosed in this application may be implemented by hardware, or may beimplemented by the processor by executing a software instruction. Thesoftware instruction may be formed by a corresponding software module.The software module may be stored in a RAM memory, a flash memory, a ROMmemory, an erasable programmable ROM (EPROM) memory, an electricallyerasable programmable ROM (EEPROM) memory, a register, a hard disk, aremovable magnetic disk, a compact disc-ROM (CD-ROM), or a storagemedium of any other form well-known in the art. For example, a storagemedium is coupled to the processor such that the processor can readinformation from the storage medium and write information into thestorage medium. Certainly, the storage medium may alternatively be acomponent of the processor. The processor and the storage medium may belocated in an ASIC. In addition, the ASIC may be located in acommunications apparatus. Certainly, the processor and the storagemedium may exist in the communications apparatus as discrete components.

All or some of the foregoing embodiments may be implemented by software,hardware, firmware, or any combination thereof. When software is used toimplement the embodiments, the embodiments may be implemented completelyor partially in a form of a computer program product. The computerprogram product includes one or more computer instructions. When thecomputer program instructions are loaded and executed on a computer, theprocedures or functions according to the embodiments of the presentdisclosure are all or partially generated. The computer may be ageneral-purpose computer, a special-purpose computer, a computernetwork, or another programmable apparatus. The computer instructionsmay be stored in a computer-readable storage medium or may betransmitted from a computer-readable storage medium to anothercomputer-readable storage medium. For example, the computer instructionsmay be transmitted from a website, computer, server, or data center toanother website, computer, server, or data center in a wired (forexample, a coaxial cable, an optical fiber, or a digital subscriber line(DSL)) or wireless (for example, infrared, radio, or microwave) manner.The computer-readable storage medium may be any usable medium accessibleby a computer, or a data storage device, such as a server or a datacenter, integrating one or more usable media. The usable medium may be amagnetic medium (for example, a floppy disk, a hard disk, or a magnetictape), an optical medium (for example, a digital versatile disc (DVD)),a semiconductor medium (for example, a solid-state drive (SSD)), or thelike.

The foregoing descriptions are merely specific implementations of thepresent disclosure, but are not intended to limit the protection scopeof the present disclosure. Any variation or replacement readily figuredout by a person skilled in the art within the technical scope disclosedin the present disclosure shall fall within the protection scope of thepresent disclosure. Therefore, the protection scope of the presentdisclosure shall be subject to the protection scope of the claims.

What is claimed is:
 1. A packet transmission method, comprising:receiving, by a session management device, first access network tunnelinformation from a base station; receiving, by the session managementdevice, second access network tunnel information from the base station;sending, by the session management device, the first access networktunnel information to a user plane device; sending, by the sessionmanagement device, the second access network tunnel information to theuser plane device; indicating, by the session management device to theuser plane device, to perform downlink packet duplication for a firstquality of service (QoS) flow; duplicating, by the user plane device inresponse to the indicating, a first downlink packet of the first QoSflow to obtain a second downlink packet; sending, by the user planedevice to the base station, the first downlink packet through a firstpath corresponding to the first access network tunnel information andconnecting the user plane device and the base station; and sending, bythe user plane device to the base station, the second downlink packetthrough a second path corresponding to the second access network tunnelinformation and connecting the user plane device and the base station.2. The method of claim 1, wherein indicating to perform downlink packetduplication comprises indicating, to perform downlink packet duplicationbased on a forwarding rule.
 3. The method of claim 2, wherein theforwarding rule comprises the first access network tunnel informationand the second access network tunnel information.
 4. The method of claim3, wherein the first path and the second path are usable for packettransmission for at least one QoS flow in a session.
 5. The method ofclaim 4, wherein the forwarding rule further comprises a service flowidentifier of the first QoS flow and a session identifier associatedwith the session.
 6. The method of claim 1, wherein the first downlinkpacket and the second downlink packet have a same sequence number and asame service flow identifier.
 7. The method of claim 1, whereinduplicating the first downlink packet comprises duplicating, by the userplane device, the first downlink packet of the first QoS flow in aGeneral Packet Radio Service Tunneling Protocol-user plane (GTP-U) layerto obtain the second downlink packet.
 8. The method of claim 1, furthercomprising: receiving, by the session management device, first corenetwork tunnel information from the user plane device; receiving, by thesession management device, second core network tunnel information fromthe user plane device; sending, by the session management device, thefirst core network tunnel information to the base station; sending, bythe session management device, the second core network tunnelinformation to the base station; and indicating, by the sessionmanagement device, the base station to perform uplink packet duplicationfor the first QoS flow.
 9. The method of claim 8, wherein the first corenetwork tunnel information and the second core network tunnelinformation triggers the base station to allocate the first accessnetwork tunnel information and the second access network tunnelinformation.
 10. The method of claim 8, further comprising: duplicating,by the base station in response to the indicating, a first uplink packetof the first QoS flow to obtain a second uplink packet; sending, by thebase station to the user plane device, the first uplink packet throughthe first path corresponding to the first core network tunnelinformation; and sending, by the base station to the user plane device,the second uplink packet through the second path corresponding to thesecond core network tunnel information.
 11. The method of claim 10,wherein the first uplink packet and the second uplink packet have a samesequence number and a same service flow identifier.
 12. The method ofclaim 10, further comprising: indicating, by the session managementdevice to the user plane device, to perform uplink packet eliminationfor the first QoS flow; receiving, by the user plane device, the firstuplink packet through the first path; receiving, by the user planedevice, the second uplink packet through the second path; andeliminating, by the user plane device in response to the indicating, thesecond uplink packet to obtain the first uplink packet.
 13. The methodof claim 12, wherein eliminating the second uplink packet compriseseliminating the second uplink packet based on a same sequence number toobtain the first uplink packet.
 14. The method of claim 12, whereinindicating the user plane device to perform uplink packets eliminationcomprises indicating to the user plane device to perform uplink packetelimination based on a forwarding rule.
 15. A system for packettransmission comprising: a session management device configured to:receive first access network tunnel information from a base station;receive second access network tunnel information from the base station;send the first access network tunnel information to the user planedevice; send the second access network tunnel information to the userplane device; and indicate the user plane device to perform downlinkpacket duplication for a first quality of service (QoS) flow; and theuser plane device configured to: duplicate, in response to theindicating, a first downlink packet of the first QoS flow to obtain asecond downlink packet; send, to the base station, the first downlinkpacket through a first path corresponding to the first access networktunnel information and connecting the user plane device and the basestation; and send, to the base station, the second downlink packetthrough a second path corresponding to the second access network tunnelinformation and connecting the user plane device and the base station,separately.
 16. The system of claim 15, wherein the session managementdevice is further configured to indicate the user plane device toperform downlink packet duplication based on a forwarding rule.
 17. Thesystem of claim 16, wherein the forwarding rule comprises the firstaccess network tunnel information and the second access network tunnelinformation.
 18. The system of claim 17, wherein the first path and thesecond path are usable for packet transmission for at least one QoS flowin a session.
 19. The system of claim 18, wherein the forwarding rulefurther comprises a service flow identifier of the first QoS flow and asession identifier associated with the session.
 20. The system of claim15, wherein the first downlink packet and the second downlink packethave a same sequence number and a same service flow identifier.
 21. Thesystem of claim 15, wherein the user plane device is further configuredto duplicate the first downlink packet of the first QoS flow in aGeneral Packet Radio System Tunneling Protocol-user plane (GTP-U) layerto obtain the second downlink packet.
 22. The system of claim 15,wherein the session management device is further configured to: receivefirst core network tunnel information from the user plane device;receive second core network tunnel information from the user planedevice; send the first core network tunnel information to the basestation; send the second core network tunnel information to the basestation; and indicate the base station to perform uplink packetduplication for the first QoS flow.
 23. The system of claim 22, whereinthe first core network tunnel information and the second core networktunnel information triggers the base station to allocate the firstaccess network tunnel information and the second access network tunnelinformation.
 24. The system of claim 22, further comprising the basestation configured to: duplicate a first uplink packet of the first QoSflow to obtain a second uplink packet in response to the indicating;send, to the user plane device, the first uplink packet flow through thefirst path corresponding to the first core network tunnel information;and send, to the user plane device, the second uplink packet through thesecond path corresponding to the second core network tunnel information.25. The system of claim 24, wherein the first uplink packet and thesecond uplink packet have a same sequence number and a same service flowidentifier.
 26. The system of claim 24, wherein the session managementdevice is further configured to indicate the user plane device toperform uplink packets elimination for the first QoS flow, wherein theuser plane device is further configured to: receive the first uplinkpacket through the first path; receive the second uplink packet throughthe second path; and eliminate the second uplink packet to obtain thefirst uplink packet in response to the indicating.
 27. The system ofclaim 26, wherein the user plane device is further configured toeliminate the second uplink packet based on a same sequence number toobtain the first uplink packet.
 28. The system of claim 26, wherein thesession management device is further configured to indicate the userplane device to perform uplink packets elimination for the first QoSflow based on a forwarding rule.